;-'■:'. 


H&* 


m 


M.: 


M. 


*m 


fS 


:*i.v: 


JB 


$8 


^:J 


0   *    Or 


; 


J*?l? 


3  0.9  /^h^fr^ 


S 


Si) 


W 


t 


3  0.'^/^ 
S  $  -si/  '< 


T1SIM  '&&±LuLM  ©IF  MrHAO^IEAo 


THE   ELEMENTS 


OP 


PHYSICAL  GEOGKAPHY, 


FOE,  THE  USE  OP 


Schools,  Academies,  and  Colleges. 


BY 

EDWIN  J.  HOUSTON",  A.M., 

PROFESSOR   OF    PHYSICAL  GEOGRAPHY  AND    NATURAL    PHILOSOPHY   IN  THE   CENTRAL    HIGH 

SCHOOL  OF  PHILADELPHIA;  PROFESSOR  OF  PHYSICS  IN   THE    FRANKLIN 

INSTITUTE  OF  THE  STATE  OF   PENNSYLVANIA. 


REVISED    EDITION. 


philadelphia: 
Published  by  Eldredge  &  Brother, 

No.  17  North  Seventh  Street. 
1892. 


A  SERIES   OF  TEXT-BOOKS 

ON 

THE    NATURAL    SCIENCES. 

By  Prof.  E.  J.  HOUSTON. 
— ii  i  m&fh*  i  ■ 

1.  Easy  Lessons  in  Natural  Philosophy. 

2.  Intermediate  Lessons  in  Natural  Philosophy. 

3.  Elements  of  Natural  Philosophy. 

4.  Elements  of  Physical  Geography. 


JWGAXIQI  IIBB/ 


The  Easy  Lessons  in  Natural  Philosophy  is  in- 
tended for  children.  It  is  arranged  on  the  "  question-and- 
answer"  plan  ;  but  the  answers,  in  almost  every  case,  con- 
tain in  themselves  a  distinct  statement  apart  from  the  ques- 
tion, thus  removing  the  objections  of  those  who  are  op- 
ponents of  the  " question-and-answer "  plan  of  teaching; 
which,  if  properly  used,  is  shown  by  experience  to  be  one 
of  the  best  methods  of  reaching  the  mind  of  a  young  child. 

The  Intermediate  Lessons  in  Natural  Philos- 
ophy is  designed  for  the  use  of  pupils  who  have  finished 
such  books  as  Houston's  "  Easy  Lessons  in  Natural  Philos- 
ophy," Martindale's  "First  Lessons  in  Natural  Philos- 
ophy," Swift's  "First  Lessons  in  Natural  Philosophy," 
Hotze's  "First  Lessons  in  Physics,"  Parker's  "Natural 
Philosophy,"  Part  I.,  Peterson's  "Familiar  Science,"  and 
other  similar  books,  but  who  are  not  sufficiently  advanced 
to  take  up  the  larger  text-books.    Its  publication  was  de- 


termined upon  at  the  request  of  teachers  in  many  parts 
of  the  country,  who  have  felt  the  need  of  a  book  of  this 
grade  to  meet  the  wants  of  their  own  classes.  So  far  as  we 
know,  there  is  no  other  book  in  the  market  which  fills  the 
want  here  indicated. 

The  Elements  of  Natural  Philosophy  is  in- 
tended for  High  Schools,  Academies,  Seminaries,  Normal 
Schools,  etc.  It  gives  the  elements  of  the  science  in  a 
concise  form  and  in  logical  sequence,  so  that  the  book 
forms  a  system  of  Natural  Philosophy,  and  not  a  mere 
collection  of  disconnected  facts.  It  is  fully  "up  to  the 
times"  in  every  respect,  and  gives  full  descriptions  of  the 
most  important  discoveries  recently  made  in  Physical 
Science.  The  Electric  Light,  the  Telephone,  the  Micro- 
phone, the  Phonograph,  etc.  are  all  described  and  illus- 
trated. Teachers  will  be  well  pleased  with  this  book.  It 
will  give  satisfaction  wherever  introduced. 


•  o<>o. 


Copyright,  1891,  by  ELDREDGE  &   BROTHER. 


Westcott  &  Thomson, 
Mectrotypers,  Philada. 


The  George  S.  Ferguson  Co, 
Printers,  Philada. 


0 
J  Ml 


Preface 


TO   THE    ORIGINAL   EDITION. 

"HD^^OO 

TN  the  preparation  of  this  work,  an  endeavor  has  been  made  to  supply  a  concise  yet  comprehensive 
■*•  text-book,  suited  to  the  wants  of  a  majority  of  our  schools. 

The  Author,  in  the  course  of  his  teaching,  has  experienced  the  need  of  a  work  in  which  unneces- 
sary details  should  be  suppressed,  and  certain  subjects  added,  which,  though  usually  omitted  in  works 
on  Physical  Geography,  seem,  in  his  judgment,  to  belong  properly  to  the  science.  The  variety  of 
topics  necessarily  included  under  the  head  of  Physical  Geography  renders  it  almost  impossible  to 
cover  the  entire  ground  of  the  ordinary  text-books  during  the  time  which  most  schools  are  able  to 
devote  to  the  study,  and  the  feeling  of  incompleted  work  thus  impressed  on  the  mind  of  both  teacher 
and  scholar  is  of  the  most  discouraging  nature. 

To  remove  these  difficulties,  the  Author,  during  the  past  few  years,  has  arranged  for  his  own 
students  a  course  of  study,  which,  with  a  few  modifications,  he  has  at  last  put  into  book  form,  thinking 
that  it  may  prove  beneficial  to  others. 

The  division  of  the  text  into  large  and  small  print  has  been  made  with  a  view  of  meeting  the 
wants  of  different  grades  of  schools,  the  large  type  containing  only  the  more  important  statements,  and 
the  small  type  being  especially  designed  for  the  use  of  the  teacher  and  the  advanced  student.  The 
maps  have  been  carefully  drawn  by  the  Author  according  to  the  standard  works  and  the  latest 
authorities.  Neither  time  nor  expense  has  been  spared  to  insure  accuracy  of  detail  and  clearness 
of  delineation. 

Throughout  the  work  no  pains  have  been  spared  to  insure  strict  accuracy  of  statement.  Clearness 
and  conciseness  have  been  particularly  aimed  at ;  for  which  reason  the  names  of  authorities  for  state- 
ments which  are  now  generally  credited  have  been  purposely  omitted. 

The  Author  has  not  hesitated  to  draw  information  from  all  the  standard  works  on  Geography, 
Physics,  Geology,  Astronomy,  and  other  allied  sciences ;  and  in  the  compilation  of  the  Pronouncing 
Vocabulary  he  acknowledges  his  indebtedness  to  Lippincott's  Gazetteer  of  the  "World. 

Acknowledgments  are  due  to  Mr.  William  M.  Spackman,  of  Philadelphia,  and  Prof.  Elihu 
Thomson,  of  the  Central  High  School,  for  critical  review  of  the  manuscript.  Also  to  Mr.  M.  Benja- 
min Snyder,  of  the  Central  High  School,  for  revision  of  the  proof-sheets  of  the  chapter  on  Mathe- 
matical Geography.  E.  J.  H. 

Central  High  School,  Philadelphia,  Pa.      — - tmtmm  jr^fiM  m 

MroUojLx  i5i 


Preface 


TO    THE    KEVISED    EDITION. 


5XKO 


rTlHE  marked  progress  which  has  been  made  in  most  of  the  departments  of  science  embraced 
in  the  study  of  Physical  Geography  since  the  issue  of  the  original  edition  of  "The 
Elements  of  Physical  Geography"  has  rendered  the  preparation  of  a  revised  edition  a  matter 
of  necessity. 

The  study  of  Physical  Geography,  including  as  it  does  not  only  the  crust  of  the  earth  and 
its  heated  interior,  but  also  the  distribution  of  its  land,  water,  air,  plants,  and  animals,  includes, 
in  its  range,  a  great  variety  of  topics,  and  necessitates  for  its  proper  elucidation  many  branches 
of  science.  Some  knowledge  of  the  elementary  principles  of  these  sciences  is  necessary  to  the 
proper  study  of  Physical  Geography.  The  number  of  such  principles  is  great,  and  the  temptation 
naturally  exists  to  encumber  even  an  elementary  text-book  with  such  an  abundance  of  leading 
principles  as  to  render  it  either  incomprehensible,  or  too  extended  for  actual  use  in  the  school- 
room. 

The  author  has  endeavored  in  the  revised  edition  to  avoid  undue  multiplicity  either  of  ele- 
mentary principles  or  unimportant  details.  His  object  has  been  to  develop  forcibly  the  close  inter- 
dependence of  the  inanimate  features  of  the  earth's  surface,  the  land,  water,  and  air,  with  its 
animate  features,  its  flora,  and  fauna,  and  to  show  the  marked  influence  which  all  of  these  exert 
on  the  development  of  the  human  race,  and,  therefore,  on  history  itself. 

Eecognizing,  from  his  standpoint  of  a  teacher,  the  inadvisability  of  crowding  a  book  with 
new  matter  simply  because  it  is  new,  the  author  has  carefully  avoided  the  introduction  of  new 
theories  unless  they  have  been  generally  accepted  by  the  best  authorities.  Old  theories  are  in  all 
cases  given  the  preference  of  new  ones,  unless  the  latter  bear  the  stamp  of  general  approval. 
At  the  same  time  the  results  of  recent  investigations  have  been  freely  given  in  all  cases  where 
they  have  been  considered  sufficiently  authoritative. 


PREFACE. 


In  order  to  avoid  confusing  the  mind  of  the  student,  controversial  matters  have  been  carefully- 
avoided.  When,  however,  opinion  on  any  subject  is  fairly  divided,  a  brief  statement  is  made  of  the 
differing  views. 

The  favorable  reception  accorded  by  the  teaching  profession  to  the  earlier  editions  of  the  book, 
and  the  flattering  increase  in  the  number  of  schools  using  it,  have  satisfied  the  author  of  the 
inadvisability  of  changing,  to  any  considerable  extent,  the  order  of  sequence  of  topics  discussed,  or 
the  general  manner  of  explanation  therein  adopted. 

In  the  preparation  of  the  revised  edition  the  author  has  freely  consulted  the  latest  standard 
authorities  in  the  many  sciences  represented. 

The  maps  have  all  been  re-drawn  according  to  the  best  authorities,  and  are  printed  and  colored 
by  processes  that  in  point  of  clearness  and  beauty  leave  little  room  for  improvement. 

EDWIN  J.  HOUSTON. 

,} 


Central  High  School, 
Philadelphia,  Jan.,  1891. 


NOTE. 


The  first  chapter  of  this  book  is  intended  mainly  for  reference,  containing  as  it  does,  m  abstract 
of  the  elementary  principles  of  Mathematical  Geography,  with  which  most  pupils  beginning  the  study 
of  Physical  Geography  are  familiar.  In  many  schools  in  which  the  book  is  used,  it  is  customary 
to  begin  the  formal  study  of  the  book  with  the  Syllabus,  page  SI,  which  presents  a  comprehensive 
review  of  the  chapter,  and  in  practice  and  results  this  plan  has  proved  satisfactory. 


Contents. 


Introductory 9 

PART  I. 

THE  EARTH  AS  A  PLANET. 

CHAPTER 

I.  Mathematical  Geography 10 

Syllabus 21 

Review  Questions 21 

PART  II. 

THE  LAND. 

Section  I. 

THE  INSIDE  OF  THE  EARTH. 

I.  The  Heated  Interior 22 

II.  Volcanoes • 23 

III.  Earthquakes 28 

Syllabus 31 

Eeview  and  Map  Questions 32 

Section  II. 

THE  OUTSIDE  OF  THE  EARTH. 

I.  The  Crust  of  the  Earth 33 

II.  Distribution  of  the  Land  Areas  ...  37 

III.  Islands 39 

IV.  Relief  Forms  of  the  Land 42 

V.  Relief  Forms  of  the  Continents  ...  45 

Syllabus      54 

Review  Questions 55 

Map  Questions , 56 


PART    III. 

THE  WATER. 

Section  I. 

CONTINENTAL.  WATERS. 

I.  Physical  Properties  of  Water 


II.  Drainage 


57 
59 


CHAPTER  PAGE 

III.  Rivers 63 

IV.  Transporting  Power  of  Rivers    ...  65 
V.  Drainage  Systems 67 

VI.  Lakes      69 

Syllabus 71 

Review  and  Map  Questions 72 

Section  II. 

OCEANIC  WATERS. 

I.  The  Ocean 73 

II.  Oceanic  Movements     75 

III.  Ocean  Currents 79 

Syllabus 83 

Review  and  Map  Questions 84 


PART  IV. 

THE  ATMOSPHERE. 

Section  I. 

THE  ATMOSPHERE. 

I.  General  Properties  of  the  Atmosphere  85 
II.  Climate      87 

III.  The  Winds 90 

IV.  Storms 96 

Syllabus 98 

Review  Questions     99 

Map  Questions 100 


Section  II. 

MOISTURE  OF  THE  ATMOSPHERE. 

I.  Precipitation  of  Moisture 101 

II.  Hail,  Snow,  and  Glaciers 107 

III.  Electrical  and  Optical  Phenomena  .  110 

Syllabus    115 

Review  Questions     116 

Map  Questions 117 


CONTENTS. 


vn 


PART  V. 

ORGANIC  LIFE. 
Section  I. 

PLANT     LIFE. 
CHAPTER  PAGE 

I.  Plant  Geography 118 

II.  Cultivated  Plants 124 

Syllabus    127 

Review  and  Map  Questions 128 

Section  II. 

ANIMAL     LIFE. 

I.  Zoological  Geography 129 

II.  Characteristic  Fauna  of  the  Conti- 
nents  133 

III.  The  Distribution  of  the  Human  Pace  135 

Syllabus     138 

Review  Questions     139 

Map  Questions 140 


PART  VI. 

THE  PHYSICAL   FEATURES  OF  THE 
UNITED  STATESr 

CHAPTER  PAGE 

I.  Surface  Structure 142 

II.  Meteorology 146 

III.  Vegetable  and  Animal  Life 151 

IV.  Agricultural  and  Mineral   Produc- 

tions      152 

V.  Alaska 156 

Syllabus 157 

Review  Questions     158 

Map  Questions 159 

GENERAL  SYLLABUS 159 

GENERAL  REVIEW  QUESTIONS     ....  162 

GENERAL  MAP  QUESTIONS     163 

PRONOUNCING  VOCABULARY 166 

BRIEF  ETYMOLOGICAL  VOCABULARY  169 
STATISTICAL  TABLES 170 


INDEX    TO    THE    MAPS. 

*o>*io° 

PAGE 

MAP  OF  VOLCANOES  AND  REGIONS  OF  EARTHQUAKES 26 

MAP  OF  OCEANIC  AREAS  AND  RIVER-SYSTEMS      68 

MAP  OF  THE  OCEAN  CURRENTS      81 

MAP  OF  THE  ISOTHERMAL  LINES 88 

MAP  OF  THE  WINDS,  RAIN,  AND  OCEAN  ROUTES     94 

MAP  SHOWING  THE  DISTRIBUTION  OF  VEGETATION 121 

MAP  SHOWING  THE  DISTRIBUTION  OF  ANIMALS ■ 131 

MAP  SHOWING  THE  DISTRIBUTION  OF  THE  RACES  OF  MEN 136 

PHYSICAL  MAP  OF  THE  UNITED  STATES 141 

MAP  SHOWING  THE  MEAN  TRACKS  OF  STORM-CENTRES,  AREAS  OF  LOW  BAROMETER 
AND  SIGNAL  FLAGS 148 


Physical  GtEOgbaphy. 


Introductory. 


1.  Geography  is  a  description  of  the  earth. 

The  earth  may  be  considered  in  three  different 
ways: 

(1.)  In  its  relations  to  the  solar  system ; 

(2.)  In  its  relations  to  government  and  society ; 

(3.)  In  its  relations  to  nature. 

Hence  arise  three  distinct  branches  of  geog- 
raphy— Mathematical,  Political,  and  Physical. 

2.  Mathematical  Geography  treats  of  the  earth 
in  its  relations  to  the  solar  system. 

Mathematical  Geography  forms  the  true  basis  for 
accurate  geographical  study,  since  by  the  view  we  thus 
obtain  of  the  earth  in  its  relations  to  the  other  members 
of  the  solar  system,  we  are  enabled  to  form  clearer  concep- 
tions of  the  laws  which  govern  terrestrial  phenomeoa. 
Here  we  learn  the  location  of  the  earth  in  space,  its  size, 
form,  and  movements,  its  division  by  imaginary  lines,  and 
the  methods  of  representing  portions  of  its  surface  on  maps. 

3.  Political  Geography  treats  of  the  earth  in 
its  relations  to  the  governments  and  societies  of 

2 


men,  of  the  manner  of  life  of  a  people,  and  of 
their  civilization  and  government. 

4.  Physical  Geography  treats  of  the  earth  in 
its  relations  to  nature  and  to  the  natural  laws  by 
which  it  is  governed.  It  treats  especially  of  the 
systematic  distribution  of  all  animate  and  inani- 
mate objects  found  on  the  earth's  surface.  It  not 
only  tells  of  their  presence  in  a  given  locality, 
but  it  also  endeavors  to  discover  the  causes  and 
results  of  their  existence. 

Physical  Geography,  therefore,  treats  of  the 
distribution  of  five  classes  of  objects — Land, 
Water,  Air,  Plants,  and  Animals. 

Geography  deals  with  the  inside  as  well  as  with  the  out- 
side of  the  earth.  It  encroaches  here  on  the  province  of 
geology.  Both  treat  of  the  earth  :  geography  mainly  with 
the  earth's  present  condition ;  geology  with  its  condition 
both  in  the  past  and  present,  though  mainly  during  the  past. 

Some  authors  make  physical  geography  a  branch  of  geol- 
ogy, and  call  it  physiographic  geology,  but  we  prefer  the 
word  "physical,"  or  as  the  etymology  would  make  it, 
"natural"  geography. 


Part  I. 

THE   EARTH   AS   A   PLANET. 


Fig.  1,    The  Earth  in  Space. 

CHAPTER   I. 

Mathematical  Geography. 

5.  The  Earth  moves  through  empty  space 
around  the  sun.  The  old  idea  of  the  earth 
resting  on,  or  being  supported  by  something,  is 
erroneous.     The  earth  rests  on  nothing. 

A  book  or  other  inanimate  object  placed  on  a 
support  will  remain  at  rest  until  something  or 
somebody  moves  it,  because  it  has  no  power  of 
self-motion.     This  property  is  called  inertia. 

Inertia  is  not  confined  to  bodies  at  rest.  If 
the  book  be  thrown  up  through  the  air,  it  ought 
to  keep  on  moving  upward  for  ever,  because  it 
has  no  more  power  to  stop  moving  than  to  begin 
to  move.  We  know,  however,  that  in  reality  it 
stops  very  soon,  and  falls  to  the  earth ;  because — 

(1.)  The  earth  draws  or  attracts  it ; 

(2.)  The  falling  body  gives  some  of  its  motion 
to  the  air  through  which  it  moves. 

Were  the  book  thrown  in  any  direction  through 
the  empty  space  in  which  the  stars  move,  it  would 
continue  moving  in  that  direction  for  ever,  unless 
it  came  near  enough  to  some  other  body  which 
would  attract  it  and  cause  it  to  change  its  motion. 

Our  earth  moves  through  empty  space  around 
the  sun,  and,  on  account  of  its  inertia,  must  con- 
tinue so  moving  for  eternities.  There  are  ample 
10 


reasons  for  believing  that  all  the  heavenly  bodies 
continue  their  motion  solely  on  account  of  their 
inertia.  The  mutual  attraction  or  gravitation  of 
neighboring  bodies  for  each  other  produces,  as 
will  be  hereafter  explained,  the  curved  paths  in 
which  they  move. 

Space  is  not  absolutely  empty,  but  is  everywhere  filled 
with  a  very  tenuous  substance  called  ether,  which  trans- 
mits to  us  the  light  and  heat  of  the  heavenly  bodies. 
Wherever  the  telescope  reveals  the  presence  of  stars  we 
must  believe  the  ether  also  extends. 

6.  The  Stars. — The  innumerable  points  of  light 
that  dot  the  skies  are  immense  balls  of  matter 
which,  like  our  earth,  are  moving  through  empty 
space.)  Most  of  them  are  heated  so  intensely  that 
they  give  off  heat  and  light  in  all  directions. 
They  are  so  far  from  the  earth  that  they  would 
not  be  visible  but  for  their  immense  size.  Beyond 
them  are  other  balls,  also  self-luminous,  but  too 
far  off  to  be  visible  except  through  a  telescope. 
Beyond  these,  again,  we  have  reason  to  believe 
that  there  are  still  others.  These  balls  of  matter 
are  called  stars.  All  the  heavenly  bodies,  how- 
ever, do  not  shine  by  their  own  light.  A  few — 
those  nearest  the  earth — shine  by  reflecting  the 
light  of  the  sun.  These  are  called  planets,  and 
move  with  the  earth  around  the  sun. 

7.  The  Solar  System  comprises  the  sun,  eight 
large  bodies  called  planets,  and,  as  far  as  now 
known,  two  hundred  and  eighty-one  smaller 
bodies  called  planetoids  or  asteroids,  besides  nu- 
merous comets  and  meteors.  Some  of  the  planets 
have  bodies  called  moons  or  satellites  moving 
around  them.  These  also  belong  to  the  solar 
system. 

Fig.  2  represents  the  solar  system.  In  the 
centre  is  the  sun.  The  circles  drawn  around 
the  sun  show  the  paths  or  orbits  of  the  planets. 
These  orbits  are  represented  as  circular,  but  in 
reality  they  are  slightly  flattened  or  elliptical. 
The  elongated  elliptical  orbits  mark  the  paths 


MATHEMATICAL    GEOGRAPHY. 


11 


NEPTUNElifif 


Fig.  2.    The  Solar  System, 


of  the  comets.  The  drawing  shows  both  the 
relative  distances  of  the  planets  and  their  sizes 
as  compared  with  each  other  and  with  the  sun, 
the  relative  size  of  the  sun  being  that  of  the 
orbit  of  Neptune. 

8.  Names  of  the  Planets. — The  planets,  named 
in  their  regular  order  from  the  sun,  beginning 
with  the  nearest,  are  as  follows — viz. :  Mercury, 
Venus,  Earth,  Mars,  Jupiter,  Saturn,  Uranus,  and 
Neptune.  The  first  four — Mercury,  Venus,  Earth, 
and  Mars — are  comparatively  small ;  the  second 
four — Jupiter,  Saturn,  Uranus,  and  Neptune — are 
very  large,  Jupiter  being  nearly  fourteen  hun- 


dred times  larger  than  the  earth.  The  initial 
letters  of  the  last  three  planets,  Saturn,  Uranus, 
and  Neptune,  taken  in  their  order  from  the  sun : 
s,  u,  and  n — spell  the  name  of  their  common 
centre. 

*  Mercury  has  a  mean  or  average  distance  of  36,000,000 
of  miles  from  the  sun ;  Venus,  67,200,000 ;  Earth,  92,900,000 ; 
and  Mars,  141,500,000. 

Jupiter  is  483,000,000:  Saturn,  886,000,000;  Uranus, 
1,781,900,000 ;  Neptune,  2,791,600,000.  The  asteroids  move 
around  the  sun  in  the  space  between  the  orbits  of  Mars  and 
Jupiter. 

*  Calculated  in  round  numbers  for  the  mean  solar  distance  of 
92,897,000  miles. 


12 


PHYSICAL    GEOGRAPHY. 


It  is  difficult  to  obtain  clear  conceptions  of  distances  that 
are  represented  by  millions  of  miles.  We  may  learn  the 
numbers,  but  in  general  they  convey  no  definite  ideas. 
Should  a  man  travel  forty  times  around  the  earth  at  the 
equator,  he  would  only  have  gone  over  about  1,000,000 
miles.  Now,  Mercury,  the  nearest  of  the  planets,  is  thirty- 
six  times  farther  from  the  sun  than  the  entire  distance  the 
man  would  have  travelled,  while  Neptune  is  nearly  three 
thousand  times  the  distance  he  would  have  travelled. 

9.  The  Satellites. — A  satellite  is  a  body  that 
revolves  around  another  body:  the  planets  are 
satellites  of  the  sun ;  the  moon  is  a  satellite  of 
the  earth.  Mars  has  two  moons.  So  far  as  is 
known,  neither  Mercury  nor  Venus  has  a  satel- 
lite. All  the  planets  whose  orbits  are  beyond  the 
orbit  of  the  earth  have  moons :  Jupiter  has  four, 
Uranus  six,  Saturn  eight,  and  Neptune  one.  Be- 
sides its  moons,  Saturn  has  a  number  of  curious 
ring-like  accumulations  of  separate  solid  or  liquid 
particles  revolving  around  it.  The  earth's  moon 
is  about  240,000  miles  from  the  earth.  Its  vol- 
ume is  about  one-forty-ninth  that  of  the  earth's. 

10.  The  Sun  is  the  great  central  body  of  the 
solar  system.  Around  it  move  the  planets  with 
their  satellites,  receiving  their  light  and  heat 
from  it.  The  sun  is  a  huge  heated  mass  about 
1,300,000  times  the  size  of  the  earth.  Its  diam- 
eter is  about  866,500  miles.  It  appears  the 
largest  self-luminous  body  in  the  heavens  because 
it  is  comparatively  near  the  earth.  Many  stars 
which  appear  as  mere  dots  of  light  are  much 
larger  than  the  sun. 

The  sun  is  a  body  heated  to  luminosity,  and  gives  out  or 
emits  light  and  heat  like  any  other  highly-heated  body. 
If  no  causes  exist  to  maintain  its  heat,  it  will  eventu- 
ally cool  and  fail  to  emit  light.  The  sun's  heat  is  partly 
kept  up  by  a  variety  of  causes,  the  principal  of  which  is 
the  heat  developed  by  meteoric  showers  that  fall  on  its 
surface.  If  a  meteor  fall  toward  the  sun  from  inter- 
planetary space,  it  will  reach  the  surface  with  enormous 
velocity,  and  its  motion  will  there  be  converted  into 
heat.  Since,  however,  the  increase  of  the  sun's  mass  so 
necessitated  is  not  confirmed  by  astronomical  observa- 
tions, it  is  believed  that  the  sun's  heat  is  not  being  main- 
tained in  this  way,  and  that  the  sun  must  eventually  cool 
— an  event,  however,  so  remote  in  time  that  the  life  of  the 
solar  system  may  be  regarded  as  practically  infinite. 

Size  of  the  Sun. — Were  the  sun  hollow  and  the  earth 
placed  at.its  centre,  there  would  not  only  be  sufficient  room 
to  enable  the  moon  to  revolve  at  its  present  actual  distance 
around  the  earth,  but  it  would  still,  in  all  parts  of  its  orbit, 
be  nearly  200,000  miles  below  the  surface  of  the  sun. 

All  the  fixed  stars  are  distant  suns,  and  probably  have 
worlds  like  our  own  moving  around  them. 

From  the  enormous  distances  of  the  fixed  stars,  we  are 
obliged,  in  estimating  their  distances,  to  use  for  our  unit 
of  measurement  the  velocity  of  light.  Any  other  common 
unit  would  be  too  small.  Light  moves  through  space  at 
the  rate  of  about  186,000  miles  a  second,  which  is  over 


11,000,000  miles  a  minute.  Notwithstanding  this  prodig- 
ious velocity,  it  would  take  over  three  thousand  years  for 
light  to  reach  the  earth  from  some  of  the  stars  that  are 
visible  to  the  naked  eye.  But  beyond  these  stars  the  tele- 
scope reveals  myriads  of  others,  whose  number  is  limited 
only  by  the  power  of  the  instrument.  We  may  conclude 
that  the  universe  is  as  boundless  as  space ;  that  is,  light 
can  never  reach  its  extreme  limits. 

11.  Cause  of  the  Earth's  Revolution. — The  earth's 
motion  through  space  is  caused  solely  by  a  projectile  force 
imparted  to  it  when  it  began  its  separate  existence,  prob- 
ably when  first  thrown  off  from  the  nebulous  sun.  From 
its  inertia  it  would  move  for  an  indefinite  time  in  one 
direction,  but  by  the  sun's  attraction  it  is  constantly 
changing  its  direction  by  falling  toward  the  sun ;  and  thus 
is  produced  the  curved  shape  of  its  orbit.  Under  the  in- 
fluence of  the  projectile  force  alone  the  earth  would  move 

b 


Fig.  3.    Cause  of  the  Curved  Shape  of  the  Earth's  Orbit. 

through  space  from  a  to  6  (Fig.  3) ;  but  during  this  time 
it  has  been  continually  changing  its  direction  by  an 
amount  equivalent  to  a  direct  fall  from  6  to  c  along  the 
line  b  d ;  hence  its  real  orbit,  during  this  time,  is  along 
the.  curved  line  from  a  to  c. 

12.  Position  of  the  Solar  System  in  Space. — 
The  sun,  with  all  the  bodies  which  move  around 
it,  is  in  that  portion  of  the  heavens  called  the 
Milky  Way.  The  sun  is  an  insignificant  star 
among  the  millions  of  other  stars  the  telescope 
has  revealed  to  us. 

It  was  formerly  believed  that  the  sun  was  stationary,  for 
it  was  not  then  known  that  the  positions  of  the  fixed  stars 
were  undergoing  slight  variations  as  regards  the  earth. 
It  is  now  generally  conceded  that  the  sun,  with  all  the 
planets,  is  moving  through  space  with  tremendous  veloc- 
ity, the  direction  at  present  being  toward  the  constella- 
tion Hercules.  The  astronomer  Maedler,  however,  believes 
that  the  grand  centre  around  which  the  solar  system  is 
moving  is  Alcyone,  the  brightest  star  in  the  constellation 
of  the  Pleiades.  The  estimated  velocity  of  the  sun  in  its 
immense  orbit  is  1,382,000,000  miles  per  year.  As  the  earth 
is  carried  along  with  the  sun  in  its  orbit,  it  is  continually 
entering  new  realms  of  space. 

13.  The  Earth.— The  shape  of  the  earth  is  that 
of  a  round  ball  or  sphere  slightly  flattened  at  two 
opposite  sides.  Such  a  body  is  termed  a  spheroid. 
There  are  two  kinds  of  spheroids — oblate  and  pro- 
late ;  the  former  has  the  shape  of  an  orange,  the 
latter  that  of  a  lemon. 


MATHEMATICAL    GEOGRAPHY. 


13 


The  straight  line  that  runs  through  the  centre 
of  a  sphere  or  spheroid  and  terminates  at  the  cir- 
cumference is  called  the  diameter.  If  the  sphere 
rotates — that  is,  moves  around  like  a  top — the 


Fig.  4,    Oblate  Spheroid.         Pig.  5.    Prolate  Spheroid. 

diameter  on  which  it  turns  is  called  its  axis.  In 
the  oblate  spheroid  the  axis  is  the  shorter  diam- 
eter ;  in  the  prolate  spheroid  the  axis  is  the  longer 
diameter. 


Fig.  6.    Curvature  of  the  Earth's  Surface. 

The  shape  of  our  earth  is  that  of  an  oblate 
spheroid.  The  polar  diameter  is  26.47  miles 
shorter  than  the  equatorial  diameter. 

14.  Proofs  of  the  Rotundity  of  the  Earth. — 


The  earth  is  so  large  a  sphere  that  its  surface 
everywhere  appears  flat.  The  following  simple 
considerations  will  prove,  however,  that  its  form 
is  nearly  spherical: 

(1.)  Appearance  of  Approaching  Objects. — If 
the  earth  were  flat,  as  soon  as  an  object  appeared 
on  the  horizon  we  would  see  the  upper  and  lower 
parts  at  the  same  time  ;  but  if  it  were  curved,  the 
top  parts  would  first  be  seen.  Now,  when  a  ship 
is  coming  into  port  we  see  first  the  topmasts,  then 
the  sails,  and  finally  the  hull ;  hence  the  earth 
must  be  curved  ;  and,  since  the  appearance  is  the 
same  no  matter  from  what  direction  the  ship  is 
approaching,  we  infer  that  the  earth  is  evenly 
curved,  or  spherical. 

(2.)  Circular  Shape  of  the  Horizon. — The  hori- 
zon— or,  as  the  word  means,  the  boundary — is  the 
line  which  limits  our  view  when  nothing  inter- 
venes. The  fact  that  this  is  always  a  circle  fur- 
nishes another  proof  that  the  earth  is  spherical. 

The  horizon  would  still  he  a  circle  if  the  earth  were 
perfectly  flat,  for  we  would  still  see  equally  far  in  all  di- 
rections ;  but  it  would  not  everywhere  be  so,  since  to  an 
observer  near  the  edges  some  other  shape  would  appear. 
It  is  on  account  of  the  spherical  form  of  the  earth  that  our 
field  of  view  on  a  plain  is  so  soon  limited  by  the  apparent 
meeting  of  the  earth  and  sky.  As  we  can  only  see  in 
straight  lines,  objects  continue  visible  until  they  reach 
such  a  distance  as  to  sink  below  the  horizon,  so  that  a 
straight  line  from  the  eye  will  pass  above  them,  meeting 
the  sky  far  beyond,  on  which,  as  a  background,  the  objects 
on  the  horizon  are  projected. 

(3.)  Shape  of  the  Earth's  Shadow. — We  can 
obtain  correct  ideas  of  the  shape  of  a  body  by 
the  shape  of  the  shadow  it  casts.  Now,  the 
shadow  which  the  earth  casts  on  the  moon  dur- 
ing an  eclipse  of  the  moon  is  always  circular, 
and  as  only  spherical  bodies  cast  circular  shad- 
ows in  all  positions,  we  infer  that  the  earth  is 
spherical. 

(4.)  Measurement. — The  shape  of  the  earth  has 
been  accurately  ascertained  by  calculations  based 
on  the  measurement  of  an  arc  of  a  meridian.  We 
therefore  not  only  know  that  the  earth  is  oblately 
spheroidal,  but  also  the  exact  amount  of  its  ob- 
lateness. 

(5.)  The  Shape  of  the  Great  Circle  of  Illumi- 
nation, or  the  line  separating  the  portions  of  the 
earth's  surface  lighted  by  the  sun's  rays  from 
those  in  the  shadow,  is  another  evidence  of  the 
rotundity  of  the  earth. 

15.  The  Dimensions  of  the  Eartfi. — The  equa- 
torial diameter  of  the  earth,  or  the  distance 
through  at  the  equator,  is,  approximately,  7926 


14 


PHYSICAL    GEOGRAPHY. 


miles ;  its  polar  diameter,  or  the  length  of  its 
axis,  is  7899  miles.  The  circumference  is  24,899 
miles.  The  entire  surface  is  equal  to  nearly 
197,000,000  square  miles. 

The  specific  gravity  of  the  earth  is  ahout  55 ;  that  is,  the 
average  weight  of  all  the  materials  that  constitute  it  is 
five  and  two-third  times  heavier  than  an  equal  volume  of 
water. 

16.  Imaginary  Circles. — In  order  to  locate 
places  on  the  earth,  as  well  as  to  represent  por- 
tions of  its  surface  on  maps,  we  imagine  the  earth 
to  be  encircled  by  a  number  of  curved  lines 
called  great  and  small  circles. 

A  great  circle  is  one  which  would  be  formed 
on  the  earth's  surface  by  a  plane  passing  through 
the  earth's  centre,  hence  dividing  it  into  two 
equal  parts.  All  great  circles,  therefore,  divide 
the  earth  into  hemispheres. 

The  formation  of  a  great  circle  on  a  sphere  by  cutting 
it  into  two  equal  parts  is  shown  in  Fig.  7. 


Fig.  7.    Great  Circle. 

The  shortest  distance  between  any  two  places  on  the 
earth  is  along  the  arc  of  a  great  circle. 

A  small  circle  is  one  formed  by  a  plane  which 
does  not  cut  the  earth  into  two  equal  parts. 

The  formation  of  a  small  circle  by  cutting  a  sphere  into 
unequal  parts  is  shown  in  Fig.  8. 


Fig.  8.    Small  Circle. 

The  great  circles  employed  most  frequently  in 
geography  are  the  equator  and  the  meridian 
circles. 

The  small  circles  are  the  parallels. 


If  we  divide  the  circumference  of  any  circle,  whether 
great  or  small,  into  three  hundred  and  sixty  equal  parts, 
each  part  is  called  a  degree.  The  one-sixtieth  part  of  a 
degree  is  a  minute;  the  one-sixtieth  part  of  a  minute  is  a 
second.  These  divisions  are  represented  as  follows :  34q, 
12',  38'' ;  which  reads,  thirty -four  degrees  twelve  minutes 
and  thirty-eight  seconds. 

The  Equator  is  that  great  circle  of  the  earth 
which  is  equidistant  from  the  poles. 

Meridian  Circles  are  great  circles  of  the  earth 
which  pass  through  both  poles. 

The  Meridian  of  any  given  place  is  that  half 
of  the  meridian  circle  which  passes  through  that 
place  and  both  poles.  A  meridian  of  any  place 
reaches  from  that  place  to  both  poles,  and  there- 
fore is  equal  to  one-half  of  a  great  circle,  and, 
with  the  meridian  directly  opposite  to  it,  forms 
a  great  circle  called  a  meridian  circle.  There 
are  as  many  meridians  as  there  are  places  on 
the  equator  or  on  any  parallel. 

In  large  cities  the  meridian  is  generally  assumed  to  pass 
through  the  principal  observatory. 


Fig,  9.    Meridians  and  Parallels. 

Parallels  are  small  circles  which  pass  around 
the  earth  parallel  to  the  equator. 

The  meridians  extend  due  north  and  south,  and  are 
everywhere  of  the  same  length  ;  the  parallels  extend  due 
east  and  west,  and  decrease  in  length  as  they  approach  the 
poles.  . 

The  Tropics  are  parallels  which  lie  23°  27' 
north  and  south  of  the  equator:  the  northern 
tropic  is  called  the  Tropic  of  Cancer,  the  south- 
ern tropic  is  called  the  Tropic  of  Capricorn. 

The  Polar  Circles  are  parallels  which  lie  23° 
27'  from  each  pole.  The  circle  in  the  Northern 
Hemisphere  is  called  the  Arctic  Circle;  that  in 
the  Southern  Hemisphere,  the  Antarctic  Circle. 

17.  Latitude  is  distance  north  or  south  from 
the  equator  toward  the  poles,  measured  along 
the  meridians.     It  is    reckoned  in  degrees. 

The  meridian  circles  are  divided  into  nearly 
equal  parts  by  the  parallels,  and  it  is  the  number 
of  these  parts  that  occur  on  the  meridian  of  any 
place  between  it  and  the  equator  which   deter- 


MATHEMATICAL    GEOGRAPHY. 


15 


mines  the  value  of  its  latitude.  If  we  conceive 
eighty-nine  equidistant  parallels  drawn  between 
the  equator  and  either  pole,  they  will  divide  all 
the  meridians  into  ninety  nearly  equal  parts ;  the 
value  of  each  of  these  parts  will  be  one  degree 
of  latitude.  Therefore,  if  the  parallel  running 
through  a  place  is  distant  from  the  equator  forty- 
five  of  these  parts,  its  latitude  is  45°.  If  more 
than  eighty-nine  parallels  be  drawn,  the  value 
©f  each  part  will  be  less  than  one  degree. 

Places  north  of  the  equator  are  in  north  lati- 
tude ;  those  south  of  it  are  in  south  latitude. 

Since  the  distance  from  the  equator  to  the  poles 
is  one-fourth  of  an  entire  circle,  and  there  are 
only  360°  in  any  circle,  90°  is  the  greatest  value 
of  latitude  a  place  can  have.  Latitude  90°  N. 
therefore  corresponds  to  the  north  pole. 

To  recapitulate :  Latitude  is  measured  on  the 
meridians  by  the  parallels. 

18.  Longitude  is  distance  east  or  west  of  any 
given  meridian. 

Places  on  the  equator  have  their  longitude  measured 
along  it ;  everywhere  else  longitude  is  measured  along  the 
parallels. 

The  meridian  from  which  longitude  is  reckoned 
is  called  the  Prime  Meridian.  Most  nations  take 
the  meridians  of  their  own  capitals  for  their  prime 
meridian.  The  English  reckon  from  the  me- 
ridian which  runs  through  the  observatory  at 
Greenwich ;  the  French  from  Paris.  In  the 
United  States  we  reckon  from  Washington. 

Any  prime  meridian  circle  divides  all  the  par- 
allels into  two  equal  parts.  A  place  situated  east 
of  the  prime  meridian  is  in  east  longitude ;  west 
of  it  is  in  west  longitude. 

Since  there  are  only  180°  in  half  a  circle,  the  greatest 
value  the  longitude  can  have  is  180° ;  for  a  place  181°  east 
of  any  meridian  would  not  fall  within  the  eastern  half  of 
the  parallel  on  which  it  is  situated,  but  in  the  western 
half;  and  its  distance,  computed  from  the  prime  meridian, 
would  be  179°  west. 

It  is  the  meridians  that  divide  the  parallels 
into  degrees  ;  therefore  longitude  is  measured  on 
the  parallels  by  the  meridians. 

19.  Value  of  Degrees  of  Latitude  and  Longi- 
tude.— As  latitude  is  distance  measured  on  the 
arc  of  a  meridian,  the  value  of  one  degree  must 
be  the  -g-g-^th  part  of  the  circumference  along  that 
meridian,  since  there  are  only  360°  in  all.  This 
makes  the  value  of  a  single  degree  approximately 
equal  to  69£  miles.  Near  the  poles  the  flattening 
of  the  earth  causes  the  value  of  a  degree  slightly 
to  exceed  that  of  one  near  the  equator. 


The  value  of  a  degree  of  longitude  is  subject 
to  great  variation.  It  is  equal  to  the  -^r^h  part 
of  the  earth's  circumference,  provided  the  place 
be  situated  on  the  equator;  otherwise,  it  is  the 
^jl^th  part  of  the  parallel  passing  through  the 
place  that  is  taken ;  and  as  the  parallels  decrease 
in  size  as  we  approach  the  poles,  the  value  of  a 
degree  of  longitude  must  likewise  decrease  as  the 
latitude  increases,  until  at  either  pole  the  longi- 
tude becomes  equal  to  zero. 

The  value  of  a  single  degree  of  longitude  on  the  equator, 

or  at  lat.  0°,  is  equal  to  about  69£  miles. 

At  latitude  45°  it  is  equal  to  about  49  miles. 
u  60o  «  «  35      » 

II  g0O  «  II  12         M 

"  90°  "  "  0      " 

Geographical  Mile.— The  sy^th  of  the  equatorial 
circumference,  or  the  one-sixtieth  of  a  degree  of  longitude 
at  the  equator,  is  called  a  nautical  or  geographical  mile. 
The  statute  mile  contains  1760  yards ;  the  geographical  or 
nautical  mile,  2028  yards.  The  nautical  mile  is  sometimes 
called  a  knot. 

20.  Map  Projections. — The  term  projection  as 
applied  to  map-drawing  means  the  various  methods 
adopted  for  representing  portions  of  the  earth's 
surface  on  the  plane  of  a  sheet  of  paper. 

The  projections  in  most  common  use  are  Merca- 
tor's,  the  orthographic,  the  stereographic,  and  the 
conical  projections.  Of  these  the  stereographic  is 
best  adapted  to  ordinary  geographical  maps,  and 
Mercator's  to  physical  maps.  All  projections 
must  be  regarded  as  but  approximations. 

1.  The  Orthographic  Projection  is  that  by  which  the 
earth's  surface  is  represented  as  it  would  appear  to  an 
observer  viewing  it  from  a  great  distance. 

2.  The  Stereographic  Projection  is  that  by  which  the 
earth's  surface  is  represented  as  it  would  appear  to  an 
observer  whose  eye  is  directly  on  the  surface,  if  he  looked 
through  the  earth  as  through  a  globe  of  clear  glass,  and 
drew  the  details  of  the  surface  as  they  appeared  projected 
on  a  transparent  sheet  of  paper  stretched  in  front  of  his 
eye  across  the  middle  of  the  earth.  There  may  be  an 
almo? .  infinite  number  of  such  projections,  according  to 
the  position  of  the  observer.  The  two  stereographic  pro- 
jections in  most  common  use  are  the  Equatorial  and  the 
Polar. 

Mercator's  Projection  represents  the  earth  on 
a  map  in  which  all  the  parallels  and  meridians 
are  straight  lines. 

Mercator's  charts  are  drawn  by  conceiving  the 
earth  to  have  the  shape  of  a  cylinder  instead  of 
that  of  a  sphere,  and  to  be  unrolled  from  this 
cylinder  so  as  to  form  a  flat  surface.  The  me- 
ridians, instead  of  meeting  in  points  at  the  north 
and  south  poles,  are  drawn  parallel  to  each  other. 
This  makes  them  as  far  apart  in  the  polar  regions 


16 


PHYSICAL    GEOGRAPHY. 


as  at  the  equator,  and  consequently  any  portion 
of  the  earth's  surface  represented  on  such  a  chart, 
if  situated  toward  the  poles,  will  be  dispropor- 


Fig.  10.    The  Earth  on  Mercator's  Projection. 


tionally  large.  In  order  to  avoid  the  distortion 
in  the  shape  of  the  land  and  water  areas,  the  dis- 
tance between  successive  parallels  is  increased  as 


they  approach  the  poles.  The  dimensions  of  the 
land  or  water,  however,  are  greatly  exaggerated 
in  these  regions.  The  immediate  polar  regions 
are  never  represented  on  such  charts,  the  poles 
being  supposed  to  be  at  an  infinite  distance. 

Mercator's  charts  are  generally  employed  for  physical 
maps,  on  account  of  the  facility  they  afford  for  showing 
direction.  The  distortion  they  produce  in  the  relative 
size  of  land  or  water  areas  must  he  carefully  borne  in 
mind,  or  wrong  ideas  of  the  relative  size  of  various  parts 
of  the  world  will  be  obtained. 

Mercator's  charts  make  bodies  of  land  and 
water  situated  near  the  poles  appear  much  larger 
than  they  really  are. 

In  an  Equatorial  Projection  of  the  entire  earth 
the  equator  passes  through  the  middle  of  each 
hemisphere,  and  a  meridian  circle  forms  the 
borders. 

In  a  Polar  Projection  of  the  entire  earth  the 


Fig.  11.    The  Earth  on  an  Equatorial  Projection. 


poles  occupy  the  centres  of  each  hemisphere,  and 
the  equator  forms  the  borders. 

In  a  Conical  Projection  the  earth's  surface  is 


represented  as  if  drawn  on  the  frustum  of  a  cone 
and  afterward  unrolled.  This  projection  is  suit- 
able where  only  portions  of  the  earth's  surface, 


Fig.  12.    The  Earth  on  a  Polar  Projection. 


and  not  hemispheres,  are  to  be  represented.  The 
cone  is  supposed  to  be  placed  so  as  to  touch  the 
earth  at  the  central  parallel  of  the  country  to  be 
represented. 


In  maps  as  ordinarily  constructed  it  is  not  true  that  the 
upper  part  is  north,  the  lower  part  south,  the  right  hand 
east,  and  the  left  hand  west,  except  in  those  on  Merca- 
tor's projection.  In  all  maps  due  north  and  south  lie  along 
the  meridians,  and  due  east  and  west  along  the  parallels,  since 


1 


MATHEMATICAL    GEOGRAPHY. 


17 


Fig.  13.    The  CoDical  Projection. 

in  most  maps  both  parallels  and  meridians  are  curved  lines. 
Therefore,  in  most  maps  due  north  and  south  and  due  east 
and  west  will  lie  along  the  meridians  and  parallels,  and 
not  directly  toward  the  top  and  bottom,  or  the  right-  and 
left-hand  side. 

21.  The  Hemispheres. — The  equator  divides  the 
earth  into  a  Northern  and  a  Southern  Hemisphere. 

The  meridian  of  long.  20°  W.  from  Greenwich 
is  generally  taken  as  the  dividing-line  between 
the  Eastern  and  Western  Hemispheres. 

22.  The  Movements  of  the  Earth ;  Rotation. — 
The  earth  turns  around  or  spins  on  an  imaginary 
diameter  called  its  axis.  This  motion  is  called  its 
rotation. 

That  the  earth  rotates  from  west  to  east  the  following 
consideration  will  show :  To  a  person  in  a  steam-car  mov- 
ing rapidly  in  any  direction,  the  fences  and  other  objects 
along  the  road  will  appear  to.be  moving  in  the  opposite 
direction :  their  motion  is  of  course  apparent,  and  is  caused 
by  the  real  motion  of  the  car.  Now,  the  motion  of  the 
sun  and  the  other  heavenly  bodies,  by  which  they  appear 
to  rise  in  the  east  and  set  in  the  west,  is  apparent,  and  is 
caused  by  the  real  motion  of  the  earth  on  its  axis;  this 
motion  must  therefore  be  from  west  to  east.  The  sun,  the 
planets,  and  their  satellites,  so  far  as  is  known,  also  turn 
on  their  axes  from  west  to  east. 

The  earth  makes  one  complete  rotation  in  about 
every  twenty-four  hours — accurately,  23  hours  56 
minutes  4.09  seconds.  The  velocity  of  its  rota- 
tion is  such  that  any  point  on  the  equator  will 
travel  about  1042  miles  every  hour.  The  veloci- 
ty of  course  diminishes  at  points  distant  from  the 
equator,  until  at  the  poles  it  becomes  nothing. 

23.  Change  of  Day  and  Night. — The  earth  re- 
ceives its  light  and  heat  from  the  sun,  and,  being 
an  opaque  sphere,  only  one-half  of  its  surface  can 
be  lighted  at  one  time.  The  other  half  is  in  dark- 
ness, since  it  is  turned  from  the  sun  toward  por- 
tions of  space  where  it  only  receives  the  dim  light 
of  the  fixed  stars.  The  boundary-line  between 
the  light  and  dark  parts  is  a  great  circle  called 
the  Great  Circle  of  Illumination.     Had  the  earth 

3 


no  motion  either  on  its  axis  or  in  its  orbit,  that 
part  of  its  surface  turned  toward  the  sun  would 
have  perpetual  day,  and  the  other  part  perpetual 
night;  but  by  rotation  different  portions  of  the 
surface  are  turned  successively  toward  and  away 
from  the  sun,  and  thus  is  occasioned  the  change 
of  day  and  night. 

24.  The  Revolution  of  the  Earth.— The  earth  has 
also  a  motion  around  the  sun,  called  its  revolution. 

The  revolution  of  the  earth  is  from  west  to  east; 
this  is  also  true  of  all  the  planets  and  asteroids, 
and  of  all  their  satellites,  except  those  of  Uranus, 
and  probably  of  Neptune. 

The  phrases  "rotation  of  the  earth  on  its  axis"  and 
"revolution  in  its  orbit"  are  often  used  in  reference  to 
the  earth's  motion ;  but  the  simple  words  "  rotation  "  and 
"  revolution  "  are  sufficient,  since  the  first  refers  only  to 
the  motion  on  its  axis,  and  the  second  only  to  the  motion 
in  its  orbit. 

The  earth  makes  a  complete  revolution  in  365 
days  6  hours  9  minutes  9.6  seconds.  This  time 
forms  what  is  called  a  sidereal  year.  The  tropical 
year,  or  the  time  from  one  March  equinox  to  the 
next,  is  somewhat  shorter,  or  365  days  5  hours  48 
minutes  49.7  seconds.  The  latter  value  is  the  one 
generally  given  for  the  length  of  the  year.  It  is 
nearly  365  J  days. 

It  will  be  found  that  the  sum  of  the  days  in  all  the 
months  of  an  ordinary  year  is  only  equal  to  365,  while  the 
true  length  is  approximately  one-quarter  of  a  day  greater. 
This  deficiency,  which  in  every  four  years  amounts  to  an 
entire  day,  is  met  by  adding  one  day  to  February  in  every 
fourth  or  leap  year.  The  exact  time  of  one  revolution, 
however,  is  some  11  minutes  less  than  6  hours.  These 
eleven  extra  minutes  are  taken  from  the  future,  and  are 
paid  by  omitting  leap  year  every  hundredth  year,  except 
that  every  400  years  leap  year  is  counted.  In  other  words, 
1900  will  not  be  a  leap  year,  since  it  is  not  divisible  by  400, 
but  the  year  2000  will  be  a  leap  year. 

The  length  of  the  orbit  of  the  earth  is  about 
577,000,000  miles.  Its  shape  is  that  of  an  el- 
lipse which  differs  but  little  from  a  circle.  The 
sun  is  placed  at  one  focus  of  the  ellipse,  and,  as 
this  is  not  in  the  centre  of  the  orbit,  the  earth 
must  be  nearer  the  sun  at  some  parts  of  its  revo- 
lution than  at  others. 

When  the  earth  is  in  that  part  of  its  orbit  which  is  near- 
est to  the  sun,  it  is  said  to  be  at  its  perihelion;  when  in 
that  part  farthest  from  the  sun,  at  its  aphelion.  The  peri- 
helion distance  is  about  90,259,000  miles ;  the  aphelion  dis- 
tance, 93,750,000  miles.  The  earth  reaches  its  perihelion 
about  January  1st. 

The  earth  does  not  move  with  the  same  rapidity  through 
all  parts  of  its  orbit,  but  travels  more  rapidly  in  perihelion 
than  in  aphelion.  Its  mean  velocity  is  about  19  miles  a 
second,  which  is  nearly  sixty  times  faster  than  the  speed 
of  a  cannon-ball.  , 


18 


PHYSICAL    GEOGRAPHY. 


25.  Laplace's  Nebular  Hypothesis.— The  uniformity 
in  the  direction  of  rotation  and  revolution  of  the  planets 
has  led  to  a  very  plausible  supposition  as  to  the  origin  of 
the  solar  system,  by  the  celebrated  French  astronomer  La- 
place. This  suppositioTi,  known  as  Laplace's  nebular  hy- 
pothesis, assumes  that,  origiually,  all  the  materials  of  which 
the  solar  system  is  composed  were  scattered  throughout 
space  in  the  form  of  very  tenuous  or  nebulous  matter.  It 
being  granted  that  this  matter  began  to  accumulate  around 
a  centre,  and  that  a  motion  of  rotation  was  thereby  ac- 
quired, it  can  be  shown,  on  strict  mechanical  principles, 
that  a  system  resembling  the  solar  system  might  be  evolved. 

As  the  mass  contracted  on  cooling,  the  rapidity  of  its 
rotation  increased.  The  equatorial  portions  bulged  out 
through  the  centrifugal  force,  until  ring-like  portions 
separated,  and,  collecting  in  spherical  masses,  formed  the 
planets.  The  planets  in  a  similar  manner  detached  their 
satellites.  At  the  time  of  the  separation  of  Neptune  the 
nebulous  sun  must  have  extended  beyond  the  orbit  of  this 
planet.  The  temperature  requisite  for  so  great  an  expan- 
sion must  have  been  enormous. 

Although  a  mere  hypothesis,  there  are  many  facts  which 
tend  to  sustain  it,  and  it  is  now  generally  accepted. 

26.  The  Plane  of  the  Earth's  Orhit  is  a  per- 
fectly flat  surface  so  placed  as  to  touch  the  earth's 
orbit  at  every  point.  It  may  be  regarded  as  an 
imaginary  plane  of  enormous  extent  on  which  the 
earth  moves  in  its  journey  around  the  sun. 

27.  Causes  of  the  Change  of  Seasons. — The 
change  of  the  earth's  seasons  is  caused  by  the 
revolution  of  the  earth,  together  with  the  fol- 
lowing circumstances: 


Fig.  14.    Inclination  of  Axis  to  Orbit  and  Ecliptic. 


(1.)  The  inclination  of  the  earth's  axis  to  the 
plane  of  its  orbit.  The  inclination  is  equal  to 
66°  33'. 

The  ecliptic  is  the  name  given  to  a  great  circle  whose 
plane  coincides  with  the  plane  of  the  earth's  orbit.  Since 
the  earth's  axis  is  90°  distant  from  the  equator,  the  plane 
of  the  ecliptic  must  be  inclined  to  the  plane  of  the  equator 
90°  minus  66°  33',  or  23°  27'. 

The  mere  revolution  of  the  earth  would  be  unable  to 
produee  a  change  of  seasons,  unless  the  earth's  axis  were 
inclined  to  the  plane  of  its  orbit.  If,  for  example,  the 
axis  of  the  earth  stood  perpendicularly  on  the  plane  of  its 
orbit,  the  sun's  rays  would  so  illumine  the  earth  that  the 
great  circle  of  illumination  would  always  be  bounded  by 
some  meridian  circle.  The  days  and  nights  would  then 
be  of  equal  length,  and  the  distribution  of  heat  the  same 
throughout  the  year.  Under  these  circumstances  there 
could  b*  no  change  of  seasons,  since  the  sun's  rays  would 


always  fall  perpendicularly  on  the  same  part  of  the  earth : 
on  the  equator. 

(2.)  The  Constant  Parallelism  of  the  Earth's 
Axis. — During  the  revolution  of  the  earth,  its 
axis  always  points  to  nearly  the  same  place  in 
the  heavens:  nearly  to  the  north  star.  It  is 
therefore  always  parallel  to  any  former  position. 

Unless  the  earth's  axis  were  constantly  parallel  to  any 
former  position,  the  present  change  of  seasons  would  not 
exist. 

On  account  of  the  spherical  form  of  the  earth, 
only  a  small  part  of  its  surface  can  receive  the 
vertical  rays  of  the  sun  at  the  same  time.  This 
part  can  be  regarded  as  nearly  a  point ;  and  since 
only  one-half  of  the  earth  is  lighted  at  any  one 
time,  the  great  circle  of  illumination  must  extend 
90°  in  all  directions  from  the  point  which  receives 
the  vertical  rays.  By  rotation  all  portions  of 
the  surface  situated  anywhere  within  the  tropics 
in  the  same  latitude,  at  some  time  or  another 
during  the  day,  are  turned  so  as  to  receive  the 
vertical  rays  of  the  sun,  and  consequently,  the 
portion  so  illumined  has  the  form  of  a  ring  or 
zone.  Other  things  being  equal,  this  zone  con- 
tains th^  hottest  portions  of  the  surface,  the  heat 
gradually  diminishing  as  we  pass  toward  either 
pole. 

On  account  of  the  inclination  of  its  axis,  the 
earth  receives  the  vertical  rays  of  the  sun  on  new 
portions  of  its  surface  every  day  during  its  revo- 
lution ;  and  it  is  because  different  portions  of  the 
surface  are  constantly  being  turned  toward  the  sun 
that  the  change  of  seasons  is  to  be  attributed. 

As  the  earth  changes  its  position  in  its  orbit,  the 
sun's  rays  fall  vertically  on  different  parts  of  the 
surface,  so  that  during  the  year  one  part  or  an- 
other of  the  surface  within  23°  27'  on  either  side 
of  the  equator  receives  the  vertical  rays. 

The  astronomical  year  begins  on  the  20th 
of  March,  and  we  shall  therefore  first  consider 
the  position  of  the  earth  in  its  orbit  at  that 
time. 

An  inspection  of  Fig.  15  will  show  that  at  this 
time  the  earth  is  so  turned  toward  the  sun  that 
the  vertical  rays  fall  exactly  on  the  equator.  The 
great  circle  of  illumination,  therefore,  reaches  to 
the  poles,  and  the  days  and  nights  are  of  an  equal 
length  all  over  the  earth.  This  time  is  called  the 
March  equinox.  Spring  then  begins  in  the  North- 
ern Hemisphere,  and  autumn  in  the  Southern. 
This  is  shown  more  clearly  in  Fig.  16,  which 
represents  the  relative  positions  of  the  illumined 
and  non-illumined  portions  at  that  time. 


MATHEMATICAL    GEOGRAPHY. 


19 


SEPTEMB  ER- 
o    EQUINOX 


DECEMBER, 
SOLSTICE? 


JUNE 
\SOLSTICE\ 


"MARCH 
EQUINOX 


April. 


Fig.  15.    The  Orbit  of  the  Earth,  showing  the  Change  of  Seasons, 


As  the  earth  proceeds  in  its  orbit,  the  inclina- 
tion of  the  axis  causes  it  to  turn  the  Northern 
Hemisphere  more  and  more  toward  the  sun.  The 
vertical  rays,  therefore,  fall  on  portions  farther 
and  farther  north  until,  on  the  21st  of  June,  the 


Fig.  16.    The  Earth  at  an  Equinox. 

vertical  rays  reach  their  farthest  northern  limit, 
and  fall  directly  on  the  Tropic  of  Cancer,  23°  27' 
N.,  when  the  sun  is  said  to  be  at  its  summer  sol- 
stice. * 

Since  the  portions  receiving  the  vertical  rays 
of  the  sun  are  now  on  the  Tropic  of  Cancer, 


the  light  and  heat  must  extend  in  the  Northern 
Hemisphere  to  23°  27'  beyond  the  north  pole,  or 
to  the  Arctic  Circle ;  while  in  the  Southern  Hemi- 
sphere they  must  fall  short  of  the  south  pole  by 
the  same  number  of  degrees,  or  reach  to  the  Ant- 


Fig.  17.    The  Earth  at  the  Summer  Solstice. 

arctic  Circle.     The  Northern  Hemisphere  then  be- 
gins its  summer,  and  the  Southern  its  winter. 

The  relative  positions  of  the  illumined  and 
non-illumined  portions  of  the  earth  at  the  sum- 
mer solstice  are  more  clearly  shown  in  Fig.  17. 
Here,  as  is  shown,  the  great  circle  of  illumination 


20 


PHYSICAL    GEOGRAPHY. 


extends  in  the  Northern  Hemisphere  as  far  over 
the  pole  as  the  Arctic  Circle. 

After  the  21st  of  June  the  Northern  Hemi- 
sphere is  turned  less  toward  the  sun,  and  the 
vertical  rays  continually  approach  the  equator, 
all  the  movements  of  the  preceding  season  being 
reversed,  until  on  the  22d  of  September,  the  time 
of  the  September  equinox,  the  equator  again  receives 
the  vertical  rays,  the  great  circle  of  illumination 
again  coinciding  with  the  meridian  circles.  The 
earth  has  now  moved  from  one  equinox  to  an- 
other, and  has  traversed  one-half  of  its  orbit. 
The  Southern  Hemisphere  then  begins  its  spring, 
the  Northern  its  autumn.    ' 

From  the  22d  of  September  until  the  20th  of 
March,  while  the  earth  moves  through  the  other 
half  of  its  orbit,  the  same  phenomena  occur  in 
the  Southern  Hemisphere  that  have  already  been 
noticed  in  the  Northern.  Immediately  after  the 
22d  of  September  the  inclination  of  the  axis 
causes  the  earth  to  be  so  turned  toward  the  sun 
that  its  rays  begin  to  fall  south  of  the  equator ; 
and,  as  the  earth  proceeds  in  its  orbit,  the  South- 
ern Hemisphere  is  turned  more  and  more  toward 
the  sun,  and  the  vertical  rays  fall  farther  and 
farther  toward  the  pole.  This  continues  until 
the  21st  of  December,  when  the  rays  fall  vertically 
on  the  Tropic  of  Capricorn,  and  the  December  sol- 
stice is  reached.  The  great  circle  of  illumination 
now  extends  beyond  the  south  pole  as  far  as  the 
Antarctic  Circle,  but  falls  short  of  the  north  pole 
23°  27',  reaching  only  the  Arctic  Circle.  Sum- 
mer then  commences  in  the  Southern  Hemisphere, 
and  winter  in  the  Northern. 

After  the  21st  of  December  the  Southern 
Hemisphere  is  turned  less  and  less  toward  the 


Fig.  18. 


S.  rFUGUJje*"^ 

Mathematical  Climatic  Zones. 


sun,  and   the   part   receiving   the  vertical   rays 
approaches   the   equator,  until  on  the   20th  of 


March  the  equator  again  receives  the  vertical 
rays,  and,  with  the  March  equinox,  spring  com- 
mences in  the  Northern  Hemisphere,  and  with 
it  a  new  astronomical  year. 

28.  Mathematical  Zones. — The  Torrid  Zone. — 
That  belt  of  the  earth's  surface  which  lies  be- 
tween the  tropics  is  called  the  Torrid  Zone. 
During  one  time  or  another  throughout  the 
year  every  part  of  its  surface  receives  the  ver- 
tical rays  of  the  sun. 

The  Temperate  Zones  are  included  between  the 
tropics  and  the  polar  circles.  The  northern  zone 
is  called  the  North  Temperate  Zone,  and  the  south- 
ern zone,  the  South  Temperate  Zone. 

The  Polar  Zones  are  included  between  the 
polar  circles  and  the  poles.  The  northern  zone 
is  called  the  North  Frigid  Zone,  and  the  southern 
zone,  the  South  Frigid  Zone. 

These  zones,  which  are  separated  by  the  parallels  of  lati- 
tude, are  generally  termed  the  astronomical  or  mathematical 
zones  to  distinguish  them  from  others  called  physical  zones, 
which  are  bounded  by  the  lines  of  mean  annual  temper- 
ature. 

It  will  be  noticed  that  the  distance  of  the  tropics  from 
the  equator  and  of  the  polar  circles  from  the  poles  is  23° 
27',  or  the  value  of  the  inclination  of  the  plane  of  the 
ecliptic  to  the  plane  of  the  equator. 

29.  Length  of  Day  and  Night.  —  Whenever 
more  than  half  of  either  the  Northern  or  South- 
ern Hemisphere  is  illumined,  the  great  circle  of 
illumination  will  divide  the  parallels  unequally, 
and  the  length  of  the  daylight  in  that  hemisphere 
will  exceed  that  of  the  night  in  proportion  as  the 
length  of  the  illumined  part,  measured  along  any 
of  the  parallels,  exceeds  that  of  the  dark  part. 

The  length  of  daylight  or  darkness  may  exceed 
that  of  one  complete  rotation  of  the  earth.  The 
great  circle  of  illumination  may  at  times  pass 
over  the  poles  as  far  beyond  them  as  23°  27'; 
and  places  situated  within  this  limit  may  remain 
during  many  rotations  exposed  to  the  rays  of  the 
sun. 

A  little  consideration  will  show  that  the  longest  day 
must  occur  at  the  poles,  since  the  poles  must  continue 
to  receive  the  sun's  rays  from  the  time  they  are  first  illu- 
mined at  one  equinox  until  the  sun  passes  through  a  sol- 
stice and  returns  to  the  other  equinox.  Nowhere,  outside 
the  polar  circles,  will  the  length  of  daylight  exceed  one 
entire  rotation  of  the  earth. 

The  length  of  the  longest  day  at  the  equator,  latitude 
0°,  is  12  hours. 

Of  the  longest  day  at  latitude  66°  33'  is  24  hours. 

Of  the  longest  day  at  latitude  67°  20'  is  one  month. 

Of  the  longest  day  at  latitude  73°  6'  is  three  months. 

Of  the  longest  day  at  the  poles,  latitude  90°,  is  six 
months. 


MATHEMATICAL    GEOGRAPHY. 


21 


SYLLABUS. 


There  are  three  kinds  of  geography — Mathematical,  Po- 
litical, and  Physical. 

Physical  Geography  treats  of  Land,  Water,  Air,  Plants, 
and  Animals. 

Geography  deals  mainly  with  the  earth  as  it  is ;  geology 
mainly  with  the  earth  as  it  was. 

The  earth  continues  its  motion  around  the  sun  in  conse- 
quence of  its  inertia. 

The  distant  stars  are  balls  of  fire  like  our  sun,  and  prob- 
ably have  worlds  resembling  ours  revolving  around  them. 

The  sun  and  the  bodies  that  revolve  around  it  consti- 
tute the  solar  system. 

The  sun  is  about  1,300,000  times  larger  than  the  earth. 

The  sun  is  a  body  heated  to  luminosity,  and  gives  out  or 
emits  light  and  heat  like  any  other  highly-heated  body. 

The  shape  of  the  earth  is  that  of  an  oblate  spheroid 
whose  equatorial  diameter  is  about  26  miles  longer  than 
its  polar.  That  the  earth  is  round  and  not  flat  is  proved 
— 1st,  by  the  appearance  of  approaching  or  receding  ob- 
jects ;  2d,  by  the  circular  shape  of  the  horizon ;  3d,  by  the 
circular  shape  of  the  earth's  shadow ;  4th,  by  actual  meas- 
urement; and  5th,  by  the  shape  of  the  great  circle  of 
illumination. 

The  earth's  diameter  is  nearly  8000  miles,  its  circumfer- 
ence not  quite  25,000  miles,  and  its  area  about  197,000,000 
square  miles. 

The  imaginary  circles  used  in  geography  are  the  Equa- 
tor, the  Meridian  Circles,  and  the  Parallels. 

Latitude  is  measured  on  the  meridians  by  the  parallels. 


The  greatest  number  of  degrees  of  latitude  a  place  can 
have  is  90° ;  the  greatest  of  longitude,  180°.  The  latitude 
at  the  equator  is  0°  N.  or  S.  The. longitude  at  the  poles  or 
on  the  prime  meridian  is  0°  E.  or  W. 

Longitude  is  measured  on  the  equator,  or  on  the  parallels, 
by  the  meridians. 

Maps  are  drawn  on  different  projections  :  the  Equatorial, 
the  Polar,  and  Mercator's  projections  are  in  most  general 
use.  A  Mercator's  projection  causes  places  near  the  poles 
to  appear  larger  than  they  really  are. 

On  all  maps  due  north  and  south  lies  along  the  merid- 
ians; due  east  and  west,  along  the  parallels:  when  these 
are  curved  lines,  the  top  and  bottom  of  the  map  will  not 
always  represent  north  and  south,  nor  the  right  and  left 
hand  east  and  west. 

The  inclination  of  the  earth's  axis  to  the  plane  of  its 
orbit,  and  the  constant  parallelism  of  the  axis  with  any 
former  position,  together  with  the  revolution  around  the 
sun,  cause  the  change  of  seasons. 

The  astronomical  year  begins  March  20th. 

On  the  20th  of  March  and  on  the  22d  of  September  the 
days  and  nights  are  of  equal  length  all  over  the  earth. 
From  the  20th  of  March  the  days  increase  in  length  in  the 
Northern  Hemisphere  until  the  21st  of  June,  when  they 
attain  their  greatest  length ;  they  then  decrease  until  the 
22d  of  September,  when  they  again  become  equal. 

The  Torrid  Zone  is  the  hottest  part  of  the  earth,  because, 
during  one  time  or  another  throughout  the  year,  every  part 
of  its  surface  receives  the  vertical  rays  of  the  sun. 


REVIEW  QUESTIONS. 


«>XKc 


The  Solar  System. 

How  does  the  principle  of  inertia  apply  to  the  earth's 
motion  around  the  sun? 

What  do  you  understand  by  the  solar  system? 

Describe  the  earth's  position  in  the  solar  system.  Which 
of  the  planets  are  between  the  earth  and  the  sun  ?  Which 
are  beyond  the  orbit  of  the  earth  ? 

How  does  the  size  of  the  sun  compare  with  that  of  the 
earth  ? 

Are  any  of  the  distant  stars  larger  than  our  sun  ? 

What  is  a  satellite  ?  Which  of  the  planets  have  satellites  ? 

Explain  the  cause  of  the  circular  shape  of  the  earth's 
orbit. 

In  what  part  of  space  is  the  solar  system  ? 

Has  our  sun  any  motion  through  space? 

Enumerate  the  proofs  of  the  rotundity  of  the  earth. 

State  accurately  the  length  of  the  equatorial  diameter 
of  the  earth ;  of  its  polar  diameter ;  of  its  circumference. 
What  is  its  area  ? 

How  many  times  heavier  is  the  earth  than  an  equally 
large  globe  of  water? 

Imaginary  Circles. 

Define  great  and  small  circles.  Name  the  circles  most 
commonly  used  in  geography. 

What  do  you  understand  by  latitude  ?  How  is  latitude 
reckoned  ?    Of  what  use  is  latitude  in  geography  ?    Why 


can  the  value  of  the  latitude  never  exceed  90°  ?  Of  what 
use  are  meridians  and  parallels  in  measuring  latitude? 

What  do  you  understand  by  longitude  ?  How  is  longi- 
tude reckoned  ?  Of  what  use  is  longitude  in  geography  ? 
Why  can  its  value  never  exceed  180°  ?  Of  what  use  are 
meridians  and  parallels  in  measuring  longitude? 

Where  is  the  value  of  a  degree  of  latitude  the  greatest  ? 
Of  a  degree  of  longitude ?    Why? 

What  effect  has  a  Mercator's  chart  on  the  appearance  of 
bodies  of  land  or  water  in  high  northern  or  southern  lati- 
tude? / 

What  is  an  equatorial  projection?  A  polar  projection? 
A  conical  projection?  What  is  the  position  of  the  poles  in 
an  equatorial  projection  ?    In  a  polar  projection  ? 

Movements  of  the  Karth. 

Prove  that  the  earth  turns  on  its  axis  from  west  to  east. 

Explain  the  cause  of  the  change  of  day  and  night. 

Define  a  sidereal  year ;  a  tropical  year.  Which  value  is 
generally  taken  for  the  length  of  the  civil  year  ? 

Describe  Laplace's  nebular  hypothesis. 

Enumerate  the  causes  which  produce  the  change  of 
seasons. 

On  what  days  of  the  year  will  the  sun's  rays  fall  verti- 
cally on  the  equator  ?  On  what  days  will  its  rays  fall  ver- 
tically on  the  Tropic  of  Cancer?  On  the  Tropic  of  Capri- 
corn? 


Part  II. 


THE   LAND. 


-«o>©^c 


Although  water  occupies  much  the  larger  portion  of  the  earth's  surface,  yet,  when  compared  with 
the  entire  volume  of  the  globe,  its  quantity  is  comparatively  insignificant ;  for  the  mean  depth  of  the 
ocean  probably  does  not  exceed  two  and  one-third  miles,  and  underneath  this  lies  the  solid  crust, 
with  its  heated  interior. 

The  crust  and  heated  interior  are  composed  of  a  variety  of  simple  and  compound  substances.  Simple 
or  elementary  substances  are  those  which  have  never  been  separated  into  components.  Compound 
substances  are  those  which  are  composed  of  two  or  more  simple  or  elementary  substances  combined 
under  the  influence  of  the  chemical  force. 


-~-z-3-jz5ZT^>f~$:^-Suz — 


Section  I. 


THE   INSIDE   OF  THE   EARTH. 


°XXc 


CHAPTER   I. 
The  Heated  Interior. 

30.  The  Proofs  of  the  Earth's  Original  Fluidity 
or  fused  condition  through  heat  are — 

(1.)  Its  Spherical  Shape,  which  is  the  shape 
the  earth  would  have  taken  had  it  been  placed 
in  space  when  in  a  melted  condition.     This  is 
the  shape  of  nearly  all  the  heavenly  bodies. 
22 


(2.)  The  fact  that  the  rocks  which  were  first 
formed  give  evidence  by  their  appearance  of 
having  been  greatly  heated.  These  rocks  are 
generally  highly  crystalline. 

(3.)  The  general  climate  of  the  earth  during 
the  geological  past  was  much  warmer  than  at 
present. 

Very  little  of  the  internal  heat  now  reaches  the  surface. 
According  to  Poisson,  all  that  escapes  would  raise  the  mean 
annual  temperature  only  ^th  of  a  degree  Fahr. 


VOLCANOES. 


23 


31.  Laplace's  Nebular  Hypothesis  agrees  very  well 
with  the  idea  of  a  former  igneous  fluidity,  since,  at  the 
time  of  its  separation  from  the  nebulous  sun,  the  earth 
must  have  had  a  temperature  sufficient  not  only  to  fuse, 
but  even  to  volatilize,  most  of  its  constituents. 

32.  Proofs  of  a  Present  Heated  Interior. — The 
following  considerations  show  that  the  inside  of 
the  earth  is  still  highly  heated: 

(1.)  The  deeper  we  penetrate  the  crust,  the 
higher  the  temperature  becomes.  Moreover,  the 
rate  of  increase,  though  varying  in  different  lo- 
calities with  the  character  of  the  materials  of  the 
crust,  is  nearly  uniform  over  all  parts  of  the  sur- 
face, the  average  value  of  the  increase  being  1° 
Fahr.  for  every  55  feet  of  descent. 

This  would  seem  to  indicate  that  the  entire 
inside  of  the  earth  is  heated,  and  that  the  heat 
increases  as  we  go  toward  the  centre. 

We  cannot,  however,  estimate  the  thickness  of  the  crust 
from  this  fact — 

1.  Because  we  have  never  penetrated  the  crust  more 
than  a  few  thousand  feet  below  the  level  of  the  sea,  and 
therefore  we  do  not  know  that  this  rate  of  increase  of 
temperature  continues  the  same: 

2.  Even  if  it  did  continue  uniform,  since  the  melting- 
point  of  solids  increases  with  the  pressure,  we  do  not 
know  what  allowance  should  be  made  for  this  increase. 

(2.)  In  all  latitudes  prodigious  quantities  of 
melted  rock  escape  from  the  interior  through 
the  craters  of  volcanoes.  The  interior,  there- 
fore, must  be  hot  enough  to  melt  rock. 

33.  Condition  of  the  Interior. — We  do  not 
know  the  condition  of  the  material  which  fills 
the  interior  of  the  earth.  It  might  be  supposed, 
since  rock  escapes  from  the  craters  of  volca- 
noes in  a  fluid  or  molten  condition,  that  the  in- 
terior is  filled  with  molten  matter ;  but  this  is 
not  necessarily  so,  since  the  enormous  pressure 
to  which  the  interior  is  subjected  would  prob- 
ably be  sufficient  to  compress  it  into  a  viscous 
or  pasty  mass,  or,  possibly,  even  to  render  it  solid. 
The  lava  which  issues  from  the  crater  of  a  vol- 
cano is  necessarily  more  mobile  than  the  interior 
of  the  earth ;  for,  coming,  as  it  does,  from  great 
depths,  it  must  grow  more  and  more  liquid  as  it 
approaches  the  surface  and  is  thus  relieved  of  its 
pressure.  Indeed,  the  most  viscous  rock  conceiv- 
able, if  highly  heated  when  ejected  from  pro- 
found depths,  would  become  comparatively  fluid 
on  reaching  the  surface. 

34.  Views  Concerning  the  Condition  of  the 
Interior. — Considerable  difference  of  opinion  ex- 
ists as  to  the  exact  condition  of  the  interior  of 
the  earth.  The  following  opinions  may  be  men- 
tioned : 


(1.)  That  the  earth  has  a  solid  centre  and 
crust,  with  a  heated  or  pasty  layer  between. 

(2.)  That  the  crust  is  solid,  but  the  interior 
highly  heated,  so  as  to  be  in  a  fused  or  pasty 
condition. 

(3.)  That  the  earth  is  solid  throughout,  but 
highly  heated  in  the  interior. 

Of  the  above  views,  the  second  is  perhaps  the 
most  tenable,  and  will  be  adopted  as  serving  in 
the  simplest  manner  to  explain  the  phenomena 
of  the  earth  arising  from  the  presence  of  a  highly 
heated  interior.  Admitting  the  crust  to  be  suf- 
ficiently thin,  and  in  such  a  condition  as  to  per- 
mit of  but  a  small  degree  of  warping,  then  all 
the  phenomena  can  be  satisfactorily  explained. 

35.  Thickness  of  the  Crust. — We  cannot  as- 
sign a  definite  limit  to  the  thickness  of  the  crust, 
since  the  portions  that  are  solid  from  having 
cooled,  most  probably  pass  insensibly  into  those 
that  are  nearly  solid  from  the  combined  influence 
of  loss  of  heat  and  increasing  pressure.  It  seems 
probable  that  the  portion  solidified  by  cooling  is 
thin,  when  compared  with  the  whole  bulk  of  the 
earth ;  in  other  words,  the  heated  interior  lies 
comparatively  near  the  surface. 

36.  Effects  of  the  Heated  Interior. — As  the 
crust  loses  its  heat  it  shrinks  or  contracts,  and, 
growing  smaller,  the  materials  of  the  interior  are 
crowded  into  a  smaller  space,  and  an  enormous 
force  is  thus  exerted,  both  on  the  interior  and  on 
the  crust  itself,  tending  either  to  change  the  shape 
of  the  crust,  to  break  it,  or  to  force  out  some  of 
the  interior.  The  following  phenomena  are  there- 
fore caused  by  the  contraction  of  the  crust : 

(1.)  Volcanoes; 
(2.)  Earthquakes; 

(3.)  Non-volcanic  igneous  eruptions ; 
(4.)  Gradual  elevations  or  subsidences  of  the 
crust. 

CHAPTER   II. 

Volcanoes. 

37.  Volcanoes. — One  of  the  most  striking  proofs 
of  the  existence  of  a  heated  interior  is  the  ejection 
of  enormous  quantities  of  melted  rock  through 
openings  in  the  crust. 

A  volcano  is  a  mountain,  or  other  elevation, 
through  which  the  materials  of  the  interior  escape 
to  the  surface.  The  opening  is  called  the  crater, 
and  may  be  either  on  the  top  or  on  the  sides  of 
the  mountain. 


24 


PHYSICAL    GEOGRAPHY. 


Fig.  19.    An  Eruption  of  Mount  Vesuvius. 

33.  Peculiarities  of  Craters. — The  crater,  as  its  name 
indicates,  is  cup-shaped.  The  rim,  though  generally  entire, 
is  sometimes  broken  by  the  force  of  the  eruption,  as  in 
Mount  Vesuvius,  where  the  eruption  in  79  A.  D. — the  first 
on  record — blew  off  the  northern  half  of  the  crater.  The 
material  thus  detached,  together  with  the  showers  of  ashes 
and  streams  of  lava,  completely  buried  the  cities  of  Her- 
culaneum  and  Pompeii,  situated  near  its  base. 

The  crater  is  often  of  immense  size.  Mauna  Loa,  on  the 
island  of  Hawaii,  has  two  craters — one  on  the  summit,  and 
the  other  on  the  mountain-side,  about  4000  feet  above  the 
sea.  The  latter — Kilauea — is  elliptical  in  shape,  and  about 
7i  miles  in  circumference ;  its  area  is  nearly  4  square  miles, 
and  its  depth,  from  600  to  1000  feet. 

Volcanic  mountains  are  of  somewhat  different 
shapes,  but  near  the  crater  the  conical  form  pre- 
dominates, and  serves  to  distinguish  these  moun- 
tains as  a  class.  The  shape  of  the  volcanic  cone 
is  caused  by  the  ejected  materials  accumulating 
around  the  mouth  of  the  crater  in  more  or  less 
concentric  layers. 

39.  The  ejected  materials  are  mainly  as  fol- 
lows : 

(1.)  Melted  Bock,  or  Lava. — Lava  varies,  not 
only  with  the  nature  of  the  materials  from  which 
it  was  formed,  but  also  with  the  conditions  under 
which  it  has  cooled,  and  the  quantity  of  air  or 
vapor  entangled  in  it.  Though  generally  of  a 
dark  gray,  it  occurs  of  all  colors ;  and  its  texture 
varies  from  hard,  compact  rock  to  porous,  spongy 
material  that  will  float  on  water. 

When  just  emitted  from  the  crater,  ordinary  lava  flows 
about  as  fast  as  molten  iron  would  on  the  same  slope.  On 
steep  mountains,  near  the  crater,  the  lava,  when  very 
hot,  may  flow  faster  than  a  horse  can  gallop  ;  but  it  soon 


cools,  and  becomes  covered  with  a  crust  that  greatly  re- 
tards the  rapidity  of  its  flow,  until  its  motion  can  only  be 
determined  by  repeated  observations. 

At  Kilauea,  jets  of  very  liquid  lava  are  sometimes 
thrown  out,  which,  falling  back  into  the  crater,  are  drawn 
out  by  the  wind  into  fine  threads,  thus  producing  what 
the  natives  call  Pele's  hair,  after  their  mythical  goddess. 

The  volume  of  the  ejected  lava  is  often  very  great.  Vol- 
canic islands  are  generally  formed  entirely  by  lava  streams. 
Hawaii  and  Iceland  were  probably  formed  entirely  of  lava 
emitted  from  uumerous  volcanic  cones. 

(2.)  Ashes  or  Cinders. — These  consist  of  minute 
fragments  of  lava  that  are  ejected  violently  from 
the  crater ;  at  night  they  appear  as  showers  of 
brilliant  sparks.  When  they  fall  directly  back 
on  the  mountain,  they  aid  in  rearing  the  cone. 
More  frequently,  they  are  carried  by  the  wind  to 
points  far  distant.  The  destructive  effects  of 
volcanic  eruptions  are  caused  mainly  by  heavy 
showers  of  ashes.  The  ashes,  when  exceedingly 
fine,  form  what  is  called  volcanic  dust 

At  the  beginning  of  an  eruption  large  frag- 
ments of  rock  are  sometimes  violently  thrown 
out  of  the  crater. 

(3.)  Vapors,  or  Gases. — The  vapor  of  water 
often  escapes  in  great  quantities  from  the  crater, 
especially  at  the  beginning  of  the  eruption.  On 
cooling,  it  condenses  and  forms  dense  clouds,  from 
which  torrents  of  rain  fall.  These  clouds,  lighted 
by  the  glowing  fires  beneath,  appear  to  be  actually 
burning,  and  thus  give  rise  to  the  erroneous  belief 
that  a  volcano  is  a  burning  mountain.  To  the 
condensation  of  this  vapor  is  probably  to  be  as- 
cribed the  lightning  which  often  plays  around  the 
summit  of  the  volcano  during  an  eruption.  Be- 
sides the  vapor  of  water,  various  gases  escape,  of 
which  sulphurous  acid  is  the  most  common. 

When  a  large  quantity  of  rain  mingles  with  the  ashes, 
torrents  of  mud  are  formed,  which  move  with  frightful 
velocity  down  the  slopes  of  the  mountain,  occasioning  con- 
siderable damage.  During  the  eruption  of  Galungung,  in 
Java,  more  than  one  hundred  villages  were  thus  destroyed. 
The  rock  that  is  formed  by  the  hardening  of  volcanic  mud 
is  called  tufa. 

40.  The  Inclination  of  the  Slopes  of  the  vol- 
canic cones  depends  on  the  nature  of  the  material 
of  which  they  are  formed.  Where  lava  is  the 
main  ingredient,  the  cone  is  broad  and  flat.  The 
inclination  of  a  lava  cone  ranges  from  3°  to  10°, 


Fig.  20.    Lava  Cone.    Inclination  from  3°  to  10°. 

according  to  the  liquidity  of  the  lava.     A  very 
stiff  lava  will  form  a  much  steeper  cone. 


VOLCANOES. 


25 


Ashes  and  cinders  form  steeper  cones,  whose 
inclinations  range  from  30°  to  45°. 


Fig,  21.    Ash  Cone.    Inclination  from  30°  to  45°. 

The  sides  of  volcanic  cones  are  often  rent  dur- 
ing the  eruption,  and  the  fissures  filled  with  lava, 
which  hardens  and  forms  rocky  ribs  called  dykes. 
Sometimes  the  central  cone  becomes  choked,  and 
secondary  or  parasitic  cones  are  formed. 


Fig.  22.    Volcanic  Dykes  and  Parasitic  Cones. 

41.  The  Cause  of  Volcanic  Eruptions. — As  the 
heated  earth  cools  and  the  crust  contracts,  the  ma- 
terials of  the  interior  are  crowded  into  a  smaller 
space,  and  an  enormous  force  is  exerted,  which 
causes  portions  of  the  interior  to  rise  from  profound 
depths  and  escape  through  openings  in  the  crust. 
These  openings  form  the  craters  of  volcanoes. 

The  principal  agency,  therefore,  which  brings 
up  the  heated  material  from  great  depths  is  the 
contraction  of  the  crust  on  cooling.  The  melted 
rock  thus  brought  into  the  volcano  may  escape — 

(1.)  By  the  pressure  of  highly-heated  gases  or 
vapors,  mainly  that  of  water,  which  throws  the 
lava  explosively  from  the  crater. 

(2.)  By  the  pressure  exerted  by  a  column  of 
liquid  lava.  Before  the  lava  can  run  over  the 
edge  of  the  crater  near  the  top  of  the  mountain, 
the  pressure  caused  by  its  weight  becomes  so  great 
that  the  sides  of  the  mountain  are  broken,  and 
the  lava  escapes  quietly  from  a  lower  opening. 

42.  Other  Explanations  of  Volcanic  Action.— The 
above  theory  of  volcanic  action  is  not  accepted  by  all  sci- 
entists. Instead  of  an  originally  heated  globe  that  has 
not  yet  completely  cooled,  it  is  asserted  by  some  that  heat 
is  now  being  produced  either  by  some  chemical  means, 
such  as  oxidation  or  hydration,  or  by  a  mechanical  crush- 
ing of  deep-seated  strata.  These  explanations  assume  that 
the  seat  of  the  lava  is  not  the  entire  interior  of  the  earth, 
but  that  it  is  purely  local,  existing  in  comparatively  shal- 


low basins  or  reservoirs  not  far  from  the  surface.  The 
peculiarities  of  distribution  of  volcanoes  would  -appear  to 
disprove  the  latter  assumption. 

43.  Volcanic*  Eruptions  may  be  divided  into 
two  classes:  explosive  and  non-explosive. 

Explosive  eruptions  are  caused  by  the  sudden 
formation  of  highly-heated  vapors. 

In  boiling  water,  drops  are  thrown  from  the 
surface  by  the  bursting  of  bubbles  of  steam. 
This  action  is  similar  to  that  of  explosive  vol- 
canic eruptions.  When  the  liquid  is  viscous, 
like  tar,  the  escaping  vapor  accumulates  in  large 
bubbles,  the  bursting  of  which  scatters  the  mate- 
rial in  all  directions. 

On  account  of  the  great  viscidity  of  some  lavas,  the 
evolved  gases  accumulate  until  considerable  force  is  ac- 
quired. At  Kilauea,  liquid  jets  are  thrown  upward  to  the 
height  of  40  feet.  With  very  viscid  lavas,  like  those  of 
Vesuvius,  bubbles  of  enormous  size  are  suddenly  formed, 
which  burst  with  almost  incredible  force.  Cases  are  on 
record  in  which  it  is  estimated  the  ashes  were  projected 
10,000  feet  above  the  mouth  of  the  crater. 

Non-explosive  eruptions  are  caused  by  the 
pressure  of  a  column  of  liquid  lava. 

In  non-explosive  eruptions  the  lava  escapes 
quietly  through  a  fissure  which  opens  in  the 
mountain's  side  by  the  pressure  exerted  by  the 
column  of  liquid  lava  in  the  crater. 

Since  a  column  of  lava  500  feet  high  exerts  a  pressure 
of  about  625  pounds  to  the  square  inch,  when  the  moun- 
tain is  high  the  pressure  against  the  sides  of  the  crater 
may  be  sufficient  to  rend  the  solid  rock. 

Vesuvius  is  an  example  of  an  explosive  eruption  ;  Kila- 
uea and  Etna,  of  non-explosive  eruptions. 

Volcanic  mountains  whose  eruptions  are  non- 
explosive  are  generally  high;  the  lava  can  thus 
accumulate  in  the  crater  until  it  forces  its  way 
through  fissures  below.  Volcanic  mountains  whose 
eruptions  are  explosive  are  generally  low. 

Volcanoes  are  of  common  occurrence  at  the 
bottom  of  the  ocean.  These  are  called  submarine 
volcanoes.  During  eruptions  their  cones  some- 
times project  above  the  water;  but  they  gene- 
rally soon  afterward  disappear. 

44.  Active  and  Extinct  Volcanoes. — Volcanoes 
may  be  classified  as  active  and  extinct. 

Active  Volcanoes  are  those  which  emit  smoke, 
vapor,  ashes,  or  lava  from  the  crater. 

By  an  active  volcano  we  do  not  mean  one  that  is  con- 
tinually in  a  state  of  eruption — ejecting  ashes  and  lava — 
but  one  from  which  at  least  smoke  or  vapor  is  escaping. 
The  crater  may  at  any  time  become  permanently  choked, 
when  the  volcano  becomes  extinct.  It  may,  however,  open 
at  any  time,  after  extended  intervals  of  rest,  when  the 
volcano  again  becomes  active. 


Page  26. 


"W^ 


3^ 


A* 


■*"> 


&f 


$ 


) 

-*X 

r«i 

V 

CQ: 

3 

% 

c 

a  U 

< 

> 

5  en 
|  z  | 

&H 

~ 

^J^ 

I1-* 

- 

s  o  $ 

Q[ 

fc> 

< 

L, ,  I 

^ 

% 


)S 


rt 


VOLCANOES. 


27 


45.  The  number  of  volcanoes  is  not  accurately 
known.  The  best  authorities  estimate  it  at  about 
672,  of  which  270  are  active.  Of  the  latter,  175 
are  on  islands,  and  95  are  on  the  coasts  of  the  con- 
tinents. 

46.  Regions  of  Volcanoes. — The  principal  vol- 
canic regions  of  the  earth  are — * 

(1.)  Along  the  Shores  of  the  Pacific,  where  an 
immense  chain  of  volcanoes,  with  but  few  breaks, 
encircles  it  in  a  huge  "Sea  of  Fire." 

On  the  Eastern  Borders,  in  the  Andean  range, 
are  the  volcanic  series  of  Chili,  Bolivia,  and  Ecua- 
dor ;  those  of  Central  America  and  Mexico ;  in 
the  United  States  are  the  series  of  the  Sierra 
Nevada  and  Cascade  ranges  and  of  Alaska ;  and 
finally,  connecting  the  system  with  Asia,  the  vol- 
canic group  of  the  Aleutian  Islands. 

On  the  Western  Borders  volcanoes  occur  in  the 
following  districts :  the  Kamtchatkan  Peninsula, 
with  its  submerged  ranges  of  the  Kurile  Islands ; 
the  Japan,  the  Loo  Choo,  and  the  Philippine 
Islands ;  the  Moluccas ;  the  Australasian  Island 
Chain,  terminating  in  New  Zealand  ;  and  finally, 
nearly  in  a  line  with  these,  the  volcanoes  of  Ere- 
bus and  Terror  on  the  Antarctic  continent. 

(2.)  In  the  Islands  of  the  Pacific. — Volcanic 
activity  is  not  wanting  over  the  bed  of  the  Pa- 
cific. The  Sandwich  Islands,  the  Society  Group, 
the  Marquesas,  Friendly  Islands,  New  Hebrides, 
Ladrones,  and  many  others,  are  volcanic. 

(3.)  Scattered  over  the  Seas  that  divide  the 
Northern  and  Southern  Continents,  or  in  their 
vicinity,  viz. :  in  the  neighborhood  of  the  Carib- 
bean Sea,  in  the  Mediterranean  and  Red  Seas, 
and  in  the  Pacific  and  Indian  Oceans  between 
Asia  and  Australia. 

In  the  neighborhood  of  the  Caribbean  Sea. — This 
region  includes  the  two  groups  of  the  Antilles  in 
the  Caribbean  Sea,  and  the  Gallapagos  Islands  in 
the  Pacific  Ocean. 

In  the  neighborhood  of  the  Mediterranean  and 
Bed  Seas. — This  region  includes  the  volcanoes  of 
the  Mediterranean  and  its  borders,  those  of  Italy, 
Sicily,  the  Grecian  Archipelago,  of  Spain,  Central 
France,  and  Germany,  together  with  those  near 
the  Caspian  and  Red  Seas. 

Between  Asia  and  Australia. — This  region  in- 
cludes the  Sunda  Islands,  Sumatra,  Java,  Sum- 
bawa,  Flores,  and  Timor,  which  contain  numerous 
craters.  In  Java  there  are  nearly  50  volcanoes, 
28  of  which  are  active,  and  there  are  nearly  as 

*  We  follow  mainly  the  classification  of  Dana. 
4 


many  in  Sumatra.,  There  are  109  volcanoes  in 
the  small  islands  near  Borneo. 

(4.)  In  the  Northern  and  Central  Parts  of  the 
Atlantic  Ocean. 

All  the  islands  in  the  deep  ocean  which  do  not 
form  a  part  of  the  continent  are  volcanic ;  as, 
for  example,  the  island  of  St.  Helena,  Ascension 
Island,  the  Cape  Verdes,  the  Canaries,  the  Azores, 
and  Iceland.  The  Cameroons  Mountains,  on  the 
African  coast  near  the  Gulf  of  Guinea,  together 
with  some  of  the  islands  in  the  gulf,  are  volcanic. 

(5.)  In  the  Western  and  Central  Parts  of  the 
Indian  Ocean. 

Volcanoes  are  found  in  Madagascar  and  in  the 
adjacent  islands.  They  also  occur  farther  south, 
in  the  island  of  St.  Paul  and  in  Kerguelen  Land, 
and  in  Kilimandjaro,  near  the  eastern  coast  of 
Africa. 

47.  Submarine  Volcanoes. — From  the  difficulty  in  ob- 
serving them,  submarine  volcanoes  are  not  so  well  known 
as  the  others.     The  following  regions  are  well  marked : 

In  the  Mediterranean  Sea,  near  Sicily  and  Greece. 

Near  the  island  of  Santorin  the  submarine  volcanic  en- 
ergy is  intense.  It  has  been  aptly  described  as  a  region 
"Where  isles  seem  to  spring  up  like  fungi  in  a  wood." 

In  the  Atlantic  Ocean ;  off  the  coast  of  Iceland ;  near 
St.  Michael,  in  the  Azores ;  and  over  a  region  in  the  nar- 
rowest part  of  the  ocean  between  Guinea  and  Brazil. 

In  the  Pacific  Ocean ;  near  the  Aleutian  Islands, 
where  two  large  mountain-masses  have  risen  from  the 
water  within  recent  time.  Near  the  Japan  Islands,  where, 
about  twenty -one  centuries  ago,  according  to  native  his- 
torians, Fusi  Yama,  the  highest  mountain  in  Japan,  rose 
from  the  sea  in  a  single  night. 

In  the  Indian  Ocean,  the  island  of  St.  Paul,  in  the 
deep  ocean  between  Africa  and  Australia,  exhibits  signs 
of  submarine  activity. 

48.  Peculiarities  of  Distribution. — Nearly  all 
volcanoes  are  found  near  the  shores  of  continents 
or  on  islands. 

The  only  exceptions  are  found  in  the  region 
south  of  the  Caspian  Sea,  and  in  that  of  the 
Thian  Shan  Mountains.  As  volcanoes  are  but 
openings  in  the  earth's  crust  which  permit  an  es- 
cape of  materials  from  the  pasty  interior,  they 
will  occur  only  where  the  crust  is  weakest.  This 
will  be  on  the  borders  of  sinking  oceans,  in  the 
lines  of  fracture  formed  by  the  gradual  separa- 
tion of  the  ocean's  bed  from  the  coasts  of  the 
continent.  The  floor  of  the  ocean  in  all  latitudes 
is  covered  with  a  layer  of  quite  cold  water,  so 
that  the  difference  in  the  amount  of  the  contrac- 
tion will  in  general  be  most  marked  on  the  bor- 
ders of  the  oceans  or  on  the  edges  of  the  conti- 
nents. 

In  most  regions  the  volcanoes  lie  along  lines 


28 


PHYSICAL    GEOGRAPHY. 


more  or  less  straight.  Lines  joining  such  a  series 
may  be  considered  as  huge  cracks  in  the  crust, 
the  volcanic  phenomena  occurring  in  their  weak- 
est places. 

The  frequent  occurrence  of  volcanoes  in  moun- 
tainous districts  is  caused  by  the  crust  being 
broken  and  flexed,  so  as  to  admit  of  an  easy 
passage  for  the  molten  rock. 

Where  one  system  of  fissures  crosses  another  the 
crust  becomes  weak,  the  openings  numerous,  and  the 
volcanic  activity  great.  The  two  antipodal  points 
of  the  Antilles  and  the  Sunda  Islands  are  excel- 
lent examples,  and  are  the  most  active  volcanic 
regions  on  the  earth. 

Efforts  have  been  made  to  show  some  connection  be- 
tween certain  states  of  the  weather  and  periods  of  vol- 
canic activity ;  but,  so  far,  these  have  amounted  to  mere 
predictions  of  coming  changes,  based  on  observations  of 
the  direction  of  upper  currents  of  air  from  the  clouds 
of  ashes  or  smoke  ejected  by  the  volcano.  No  law  of 
periodicity  of  eruption  has,  as  yet,  been  discovered. 

49.  Other  Volcanic  Phenomena : 

Mud  Volcanoes  are  small  hillocks  that  emit 
streams  of  hot  mud  and  water  from  their  craters, 
but  never  molten  rock.  They  are  found  in  vol- 
canic regions. 

Solfataras  are  places  where  sulphur  vapors  es- 
cape and  form  incrustations.  They  occur  in  vol- 
canic regions. 

Geysers  are  sometimes  ranked  with  volcanic  phe- 
nomena.    They  are  described  under  Hot  Spriugs. 


D^KC 


CHAPTER   III. 

Earthquakes. 

50.  Earthquakes  are  shakings  of  the  earth's 
crust,  of  degrees  varying  in  intensity  from 
scarcely  perceptible  tremors  to  violent  agita- 
tions that  overthrow  buildings  and  open  huge 
fissures  in  the  ground.  They  may  therefore  be 
divided  into  two  classes: 

(1.)  A  shaking  movement  without  any  perma- 
nent change  in  the  surface ; 

(2.)  A  shaking  movement  accompanying  an 
uplift  or  subsidence. 

An  earthquake  is  sometimes  called  a  seismic 
shock. 

,51.  Facts  concerning  Earthquakes. — A  careful 
study  of  earthquakes  appears  to  establish  the  fol- 
lowing facts : 

(1.)  The  place  or  origin  of  the  shock  is  not 
deep-seated  or  far  below  the  earth's  surface,  but 


Fig.  23,    Fissures  produced  by  the  Charleston  Earthquake  of  1886. 

is  near  the  surface,  probably  never  deeper  than 
thirty  miles,  and  often  much  less. 

(2.)  The  area  of  disturbance  depends  not  only 
on  the  energy  of  the  shock,  but  also  on  the  depth 
of  its  origin  below  the  surface :  the  deeper  the 
origin,  the  greater  the  area. 

(3.)  The  shape  of  the  origin  is  generally  that 
of  a  line,  often  many  miles  in  length. 

(4.)  The  direction  of  the  motion  at  the  surface 
is  nearly  upward  over  the  origin,  and  more  in- 
clined as  the  distance  from  the  origin  increases. 

(5.)  The  shape  of  the  area  of  disturbance  de- 
pends on  the  nature  of  the  materials  through 
which  the  wave  is  moving.  If  these  are  of 
nearly  uniform  elasticity  in  all  directions,  the 
area  is  nearly  circular;  if  more  elastic  in  one 
direction  than  in  another,  the  area  is  irregular 
in  shape. 

52.  The  Varieties  of  Earthquake  Motion  at  the 
Earth's  Surface  are — 

(1.)  A  wave-like  motion,  in  which  the  ground 
rises  and  falls  like  waves  in  water. 

(2.)  An  upward  motion,  somewhat  similar  to 
that  which  follows  an  explosion  of  powder  below 
the  surface.  This  has  been  known  to  occur  with 
sufficient  force  to  throw  heavy  bodies  considerable 
distances  up  into  the  air. 

(3.)  A  rotary  motion,  which,  from  its  destruc- 
tive effects,  is  fortunately  of  rare  occurrence. 

Humboldt  mentions  an  earthquake  that  happened  in 
Chili  where  the  ground  was  so  shifted  that  three  great 


EARTHQUAKES. 


29 


palm  trees  were  twisted  around  one  another  like  willow 
wands. 

There  are  two  kinds  of  movement  transmitted  through 
the  crust  during  earthquakes:  these  are  the  earthquake 
motion  proper,  and  the  motion  that  produces  the  accompanying 
sounds. 

53.  The  Velocity  of  Earthquake  Motion  varies 
according  to  the  intensity  of  the  shock  and  the  na- 
ture of  the  material  through  which  it  is  trans- 
mitted. No  average  result  can  therefore  be 
given.  Various  observers  have  estimated  it  at 
from  8  to  30  miles  per  minute. 

54.  The  Sounds  Accompanying  Earthquakes 
vary  both  in  kind  and  intensity.  Sometimes 
they  resemble  the  hissing  noises  heard  when  red- 
hot  coals  are  thrown  into  water ;  sometimes  they 
are  rumbling,  but  more  frequently  they  are  of 
greater  intensity,  and  are  then  comparable  to 
discharges  of  artillery  or  peals  of  thunder. 

The  confused  roaring  and  rattling  are  probably  caused 
by  the  different  rates  of  transmission  of  the  sound  through 
the  air  and  rocks. 

55.  Duration  of  the  Shocks. — When  the  area 
of  disturbance  is  large,  shocks  of  varying  intensity 
generally  follow  each  other  at  irregular  intervals. 
Though,  in  general,  the  violence  of  the  shock  is 
soon  passed,  disturbances  may  occur  at  intervals 
of  days,  weeks,  or  even  years. 

During  the  earthquake  in  Calabria  in  1783,  when  nearly 
100,000  persons  perished,  the  destructive  vibrations  lasted 
scarcely  two  minutes,  but  the  tremblings  of  the  crust  con- 
tinued long  afterward.  During  the  earthquake  at  Lisbon 
in  1755,  when  about  the  same  number  perished,  the  shock 
which  caused  the  greatest  damage  continued  but  five  or 
six  seconds,  while  a  series  of  terrible  movements  followed 
one  another  at  intervals  during  the  space  of  five  minutes. 

56.  Cause  of  Earthquakes. — It  is  generally  be- 
lieved that  the  principal  cause  of  earthquakes  is  the 
force  produced  by  the  contraction  of  a  cooling  crust. 

During  the  cooling  of  the  earth  the  crust  con- 
tinually contracts,  and  the  pressure  so  produced, 
slowly  accumulating  for  years,  at  last  rends  it 
in  vast  fissures,  thus  producing  those  violent 
movements  of  its  crust  called  earthquakes.  If 
this  theory  be  admitted — and  it  is  a  probable  one 
— the  earth's  crust  must  every  now  and  then  be 
in  such  a  strained  condition  that  the  slightest 
increase  of  force  from  within,  or  of  diminished 
resistance  from  without,  would  disturb  the  con- 
ditions of  equilibrium,  and  thus  result  in  an 
earthquake. 

57.  Strain  Caused  by  Contraction  consequent  on 
cooling  is  well  exhibited  in  the  so-called  "Prince  Ru- 
pert's Drops,"  which  are  made  by  allowing  melted  glass 
to  fall  in  drops  through  cold  water.    The  sudden  cooling 


of  the  outside  produces  powerful  forces,  which  tend  to 
compress  the  drop;  but,  since  these  forces  balance  one 
another,  no  movement  occurs  until,  by  breaking  off  the 
long  end  of  the  drop,  one  set  of  forces  is  removed,  when 
the  others,  no  longer  neutralized,  tear  the  drop  into  almost 
countless  pieces. 

Similar  effects  are  produced  by  unequal  contraction  and 
expansion.  Hot  water  poured  into  a  tumbler  will  often 
crack  it.  The  crackling  sound  of  a  stovepipe  when  sud- 
denly heated  or  cooled  is  a  similar  effect. 

58.  Other  Causes  of  Earthquakes.  —  Earth- 
quakes may  also  be  occasioned  by — 

(1.)  The  sudden  evolution  of  gases  or  vapors 
from  the  pasty  interior. 

This  is  probably  the  cause  of  many  of  the 
slight  shocks  that  occur  in  the  neighborhood  of 
active  volcanic  regions. 

(2.)  Shocks  caused  by  falling  masses. 

Those  who  deny  the  existence  of  a  pasty  interior,  en- 
deavor to  explain  the  production  of  earthquakes  by  the 
shock  caused  by  the  occasional  caving  in  of  huge  masses 
of  rocks,  in  caverns  hollowed  out  by  the  action  of  subter- 
ranean waters ;  or  by  the  gradual  settling  of  the  upturned 
strata  in  mountainous  districts.  There  can  be  no  doubt 
that  even  moderately  severe  shocks  are  caused  by  falling 
masses ;  but  such  a  force  is  utterly  inadequate  to  produce 
a  shock  like  that  which  destroyed  Lisbon,  when  an  area 
of  nearly  7,500,000  square  miles  was  shaken. 

59.  Periodicity  of  Earthquakes. — It  was  for- 
merly believed  that  earthquakes  occurred  with- 
out any  regularity,  but  by  a  comparison  of  the 
times  of  occurrence  of  a  great  number  it  has  been 
discovered  that  they  occur  more  frequently — 

(1.)  In  winter  than  in  summer ; 

(2.)  At  night  than  during  the  day ; 

(3.)  During  the  new  and  full  moon,  when  the 
attractive  force  of  the  sun  and  moon  acts  simul- 
taneously on  the  same  parts  of  the  earth. 

Earthquake  shocks  are  more  frequent  in  winter, 
and  during  the  night,  because  the  cooling,  and 
consequent  contraction,  occur  more  rapidly  at 
these  times,  and  therefore  the  gradually  accumu- 
late g  force  is  more  apt  to  acquire  sufficient  inten- 
sity to  rend  the  solid  crust. 

Earthquakes  are  more  frequent  during  new 
and  full  moon,  because  the  increased  force  on 
the  earth's  crust  caused  by  the  position  of  the 
sun  and  moon  at  these  times,  is  then  added  to 
the  accumulated  force  produced  by  cooling. 

It  has  been  asserted  that  in  the  equatorial  regions  earth- 
quakes are  especially  frequent  during  the  setting  in  of 
periodical  winds  called  the  monsoons,  at  the  change  of 
the  rainy  season  or  during  the  prevalence  of  hurricanes. 
These  facts,  however,  are  not  well  established. 

60.  Distribution  of  Earthquakes.  —  Earth- 
quakes may  occur  in  any  part  of  the  world,  but 


30 


PHYSICAL    GEOGKAPHY. 


are  most  frequent  in  volcanic  districts.  They  are 
more  frequent  in  mountainous  than  in  flat  coun- 
tries. They  are  especially  frequent  in  the  high- 
est mountains.  According  to  Huxley,  fairly  pro- 
nounced earthquake  shocks  occur  in  some  part  of 
the  earth  at  least  three  times  a  week. 

There  is,  in  many  instances,  an  undoubted  connection 
between  volcanic  eruptions  and  earthquakes.  Humboldt 
relates  that  during  the  earthquake  at  Kiobarnba,  when 
some  40,000  persons  perished,  the  volcano  of  Pasto  ceased 
to  emit  its  vapor  at  the  exact  time  the  earthquake  began. 
The  same  is  related  of  Vesuvius  at  the  time  of  the  earth- 
quake at  Lisbon. 

61.  Phenomena  of  Earthquakes. — In  order  to  give 
some  idea  of  the  phenomena  by  which  severe  earthquake 
shocks  are  attended,  we  append  a  brief  description  of  the 
earthquake  which  destroyed  the  city  of  Lisbon,  on  the  1st 
of  November,  1755.  The  loss  of  life  on  this  occasion  was 
the  more  severe,  since  the  shock  occurred  on  a  holy  day, 
when  nearly  the  whole  population  was  assembled  in  the 
churches.  A  sound  like  thunder  was  heard,  and,  almost 
immediately  afterward,  a  series  of  violent  shocks  threw 
down  nearly  every  building  in  the  city.  Many  who  es- 
caped the  falling  buildings  perished  in  the  fires  that  soon 
kindled,  or  were  murdered  by  lawless  bands  that  after- 
ward pillaged  the  city. 

The  ground  rose  and  fell  like  the  waves  of  the  sea ;  huge 
chasms  were  opened,  into  which  many  of  the  buildings 
were  precipitated.  In  the  ocean  a  huge  wave,  over  50  feet 
high,  was  formed,  which,  retreating  for  a  moment,  left  the 
bar  dry,  and  then  rushed  toward  the  land  with  frightful 
force.  This  was  repeated  several  times,  and  thousands 
perished  from  this  cause  alone.  The  neighboring  moun- 
tains, though  quite  large,  were  shaken  like  reeds,  and 
were  rent  and  split  in  a  wonderful  manner. 

This  earthquake  was  especially  remarkable  for  the  im- 
mense area  over  which  the  shock  extended.  It  reached 
as  far  north  as  Sweden.  Solid  mountain-ranges — as,  for 
example,  the  Pyrenees  and  the  Alps — were  severely  shaken. 
A  deep  fissure  was  opened  in  France.  On  the  south,  the 
earthquake  waves  crossed  the  Mediterranean  and  destroyed 
a  number  of  villages  in  the  Barbary  States.  On  the  west, 
the  waves  traversed  the  bed  of  the  Atlantic,  and  caused 
unusually  high  tides  in  the  West  Indies.  In  North  Amer- 
ica the  movements  were  felt  as  far  west  as  the  Great  Lakes. 
Feebler  oscillations  of  the  ground  occurred  at  intervals  for 
several  weeks  after  the  main  shock. 

62.  Non-volcanic  Igneous  Eruptions. — In  re- 
gions remote  from  volcanoes,  melted  rock  has 
been  forced  up  from  the  interior  through  fissures 
in  the  rocks  of  nearly  all  geological  formations. 
On  cooling,  the  mass  forms  what  is  called  a  dyke. 
Dykes  vary  in  width  from  a  few  inches  to  several 
yards.  They  are  generally  much  harder  than  the 
rocks  through  which  they  were  forced,  and,  being 
less  subject  to  erosion,  often  project  considerably 
above  the  general  surface. 

From  their  mode  of  formation,  dykes  are  gen- 
erally without  traces  of  stratification,  but  by  cool- 
ing a  series  of  transverse  fractures  are  sometimes 


produced.    The  dykes  thus  obtain  the  appearance 
of  a  series  of  columns,  called  basaltic  columns. 

Igneous  rocks  of  this  description  are  found  in 
all  parts  of  the  continents,  but  are  especially  com- 
mon near  the  borders  of  mountainous  districts. 
Fingal's  Cave,  in  Scotland,  is  a  noted  example 
of  basaltic  columns. 


Fig.  24.    Basaltic  Columns,  Fingal's  Cave,  Scotland, 

63.  Gradual  Elevations  and  Subsidences. — Be- 
sides the  sudden  changes  of  level  produced  by 
earthquakes,  there  are  others  that  take  place 
slowly,  but  continuously,  by  which  large  portions 
of  the  surface  are  raised  or  lowered  from  their 
former  positions.  The  rate  of  movement  is  very 
slow — probably  never  exceeding  a  few  feet  in  a 
century.  The  following  examples  are  the  most 
noted : 

The  Scandinavian  peninsula  (Norway  and  Swe- 
den) is  slowly  rising  in  the  north  and  sinking  in 
the  soidh. 

The  southern  part  of  the  coast  of  Greenland  is 
sinking. 

The  North  American  coast,  from  Labrador  to 
New  Jersey,  is  rising. 

The  Andes  Mountains,  especially  near  Chili, 
are  gradually  rising. 

The  Pacific  Ocean,  near  the  centre,  is  sinking 
over  an  area  of  more  than  6000  miles. 

The  cause  of  these  movements  is  to  be  traced 
to  the  warping  action  caused  by  gradual  contrac- 
tion of  a  cooling  crust. 


SYLLABUS. 


31 


SYLLABUS. 


dXKc 


The  earth  was  originally  melted  throughout.  It  after- 
ward cooled  on  the  surface  and  formed  a  crust.  The  earth's 
original  fluidity  is  rendered  probable — 

(1.)  By  the  spherical  shape  of  the  earth ; 

(2.)  By  the  crystalline  rocks  underlying  all  others; 
and 

(3.)  By  the  greater  heat  of  the  earth  during  geological 
time. 

The  interior  is  still  in  a  highly-heated  condition.  This 
is  proved — 1st.  By  the  increased  heat  of  the  crust  as  we  go 
below  the  surface ;  2d.  By  the  escape  of  lava  from  volca- 
noes in  all  latitudes. 

The  following  opinions  are  held  concerning  the  condi- 
tion of  the  interior  of  the  earth  : 

(1.)  That  the  earth  has  a  solid  centre  and  crust,  with  a 
heated  layer  between. 

(2.)  That  the  earth  has  a  solid  crust  only,  and  an  inte- 
rior sufficiently  heated  to  be  in  a  fused  or  in  a  pasty  con- 
dition. 

(3.)  That  the  earth  is  solid  throughout,  but  highly 
heated  in  the  interior. 

The  thickness  of  the  crust  is  not  known.  It  is  probable 
that  the  portions  solidified  by  cooling  pass  insensibly  into 
those  that  are  nearly  solid  from  the  combined  influence 
of  loss  of  heat  and  increasing  pressure.  The  heated 
interior,  however,  must  lie  comparatively  near  the  sur- 
face. 

The  effects  produced  by  the  heated  interior  on  the  crust 
are — 1st.  Volcanoes;  2d.  Earthquakes;  3d.  Non-volcanic 
igneous  eruptions;  and  4th.  Gradual  elevations  or  subsi- 
dences. 

Volcanic  mountains  are  of  a  variety  of  shapes.  Near 
their  craters  the  cone  shape  predominates,  and  serves  to 
distinguish  these  mountains  as  a  class. 

The  ejected  materials  of  volcanoes  are — 1st.  Melted  rock 
or  lava;  2d.  Ashes  or  cinders;  3d.  Vapors  or  gases. 

These  materials  are  brought  up  from  great  depths  into 
the  volcanic  mountain  by  the  force  produced  by  a  contract- 
ing globe.  They  may  escape  from  the  crater — 1st.  By  the 
pressure  of  highly-heated  vapors;  or,  2d.  By  the  pressure 
of  a  column  of  melted  lava. 

The  inclination  of  the  slopes  of  the  volcanic  cone  de- 
pends on  the  materials  of  which  it  is  composed.  Ash- 
cones  are  steeper  than  those  formed  of  lava. 

Eruptions  are  of  two  kinds,  explosive  and  non-explo- 
sive. 

High  volcanic  mountains  are,  as  a  rule,  characterized  by 
non-explosive  eruptions. 

Volcanoes  occur  both  on  the  surface  of  the  land  and  on 
the  bed  of  the  ocean. 

Those  on  the  land  occur  mainly  near  the  borders  of 
sinking  oceans,  where  the  crust  is  weakest. 

The  principal  volcanic  districts  of  the  world  are — 1. 
Along  the  shores  of  the  Pacific;  2.  On  the  islands  which 
are  scattered  over  the  Pacific;  3.  Scattered  over  the  seas 
which  divide  the  northern  and  southern  continents;  4.  In 
the  northern  and  central  parts  of  the  Atlantic  Ocean ;  5. 
In  the  western  and  central  parts  of  the  Indian  Ocean. 

The  centres  of  volcanic  activity  are  found  in  the  An- 
tilles and  in  the  Sunda  Islands,  where  several  lines  of 
fracture  cross  each  other. 


Subordinate  volcanic  phenomena  are  seen  in — 1.  Mud 
volcanoes;  2.  Solfataras;  3.  Geysers. 

Earthquakes  are  shakings  of  the  earth's  crust ;  they  may 
occur  with  or  without  a  permanent  displacement. 

The  following  facts  have  been  discovered  as  to  earth- 
quakes : 

(1.)  Their  place  of  origin  is  not  very  deep-seated. 

(2.)  The  area  of  disturbance  increases  with  the  energy 
of  the  shock  and  the  depth  of  the  origin. 

(3.)  The  shape  of  the  origin  is  that  of  a  line,  and  not 
that  of  a  point. 

(4.)  The  shape  of  the  area  of  disturbance  depends  on 
the  elasticity  of  the  materials  through  which  the  shock 
moves. 

(5.)  The  earthquake  motion  travels  through  the  earth 
as  spherical  waves  which  move  outward  in  all  directions 
from  the  origin  of  the  disturbance. 

The  movement  at  the  earth's  surface  may  be — 1st.  In 
the  form  of  a  gentle  wave ;  2d.  An  upward  motion ;  3d.  A 
rotary  motion. 

The  velocity  with  which  the  earthquake  motion  is  trans- 
mitted varies  with  the  intensity  of  the  shock  and  the 
nature  of  the  materials  through  which  it  is  propagated. 

There  are  two  distinct  kinds  of  motion  accompanying 
earthquake  waves :  the  earthquake  motion  proper,  and 
the  motion  producing  the  accompanying  sounds. 

As  a  rule,  the  earthquake  shocks  which  produce  the 
greatest  damage  are  of  but  short  duration,  generally  but 
a  few  seconds  or  minutes,  slighter  disturbances  may  fol- 
low the  main  shock  at  i-iteryals  of  days,  weeks,  or  even 
years. 

Earthquake  shocks  are  more  frequent — 1st.  In  winter 
than  in  summer;  2d.  At  night  than  during  the  day ;  3d. 
During  the  time  of  new  and  full  moon  than  at  any  other 
phase. 

Earthquakes  are  mainly  caused  by  the  gradually  in- 
creasing force  produced  by  the  contraction  of  the  crust. 

Earthquakes  are  also  to  be  attributed  to  the  forces  which 
eject  the  molten  matter  from  the  craters  of  volcanoes. 

Slight  earthquake  shocks  may  be  occasioned  by  the  fall- 
ing in  of  masses  of  rock  from  the  roofs  of  subterranean 
caverns,  or  by  the  settling  of  upturned  strata. 

Earthquakes  may  occur  in  any  part  of  the  earth,  but  are 
most  frequent  in  volcanic  and  in  mountainous  regions. 

Dy  ves  are  masses  of  rock  formed  by  the  gradual  cooling 
of  melted  matter  which  has  been  forced  up  through  fis- 
sures from  the  interior. 

Basaltic  columns  are  formed  by  dykes.  They  owe  their 
columnar  structure  to  fractures  produced  on  cooling. 

The  crust  of  the  earth  is  subject  to  gradual  as  well  as  to 
sudden  changes  of  level. 

The  Scandinavian  peninsula  is  rising  on  the  north  and 
sinking  on  the  south. 

The  southern  coast  of  Geeenland  is  sinking. 

The  North  American  coast,  from  Labrador  to  New  Jer- 
sey, is  rising. 

The  range  of  the  Andes  near  Chili  is  rising. 

The  bed  of  the  Pacific  in  the  neighborhood  of  the  Poly- 
nesian island  chain  is  sinking. 

These  movements  are  caused  by  the  contraction  of  a 
cooling  crust. 


32 


PHYSICAL    GEOGRAPHY. 


REVIEW   QUESTIONS. 


►o^c 


The  Heated  Interior. 

Enumerate  the  proofs  that  the  interior  of  the  earth  is 
still  in  a  highly-heated  condition. 

Name  some  circumstances  which  render  it  probable  that 
the  earth  was  originally  melted  throughout. 

What  is  the  average  rate  of  increase  of  temperature 
with  descent  below  the  surface  ? 

How  can  it  be  shown  that  the  whole  interior  of  the 
earth  is  filled  with  highly-heated  matter? 

Why  is  it  so  difficult  to  assign  a  definite  limit  to  the 
thickness  of  the  earth's  crust? 

Is  the  interior  of  the  earth  supposed  to  be  in  as  fluid  a 
condition  as  that  of  the  lava  which  escapes  from  a  volcano  ? 

What  four  classes  of  effects  are  produced  in  the  crust  by 
the  heated  interior  ? 

Volcanoes. 

What  are  volcanoes  ?  What  connection  have  they  with 
the  interior  of  the  earth  ?  How  do  active  volcanoes  differ 
from  those  which  are  extinct  ? 

Explain  the  origin  of  the  conical  form  of  volcanic 
mountains. 

Which  generally  produces  the  more  destructive  effects, 
ashes  or  lava?    Why? 

Enumerate  the  materials  which  are  ejected  from  the  in- 
terior of  the  earth  through  the  craters  of  volcanoes. 

What  is  tufa  ?     How  is  it  formed  ? 

Which  has  the  greater  inclination,  a  lava-cone  or  an 
ash-cone  ? 

Explain  in  full  the  manner  in  which  the  shrinkage,  or 
contraction  of  the  earth  on  cooling,  produces  a  pressure 
both  in  the  interior  and  in  the  crust. 

By  what  forces  are  volcanic  eruptions  produced? 

Into  what  two  classes  may  all  volcanic  eruptions  be  di- 
vided ?    How  are  those  of  each  class  caused  ? 


Give  an  example  of  each  of  these  classes. 

What  is  the  highest  volcano  in  the  world? 

Under  what  five  regions  may  all  the  volcanoes  in  the 
world  be  arranged? 

In  what  parts  of  the  world  are  volcanoes  most  numer- 
ous? 

Why  are  volcanoes  more  numerous  here  than  elsewhere  ? 

Name  some  of  the  regions  of  submarine  volcanoes. 

Why  are  all  volcanoes  found  near  the  coasts  of  the  con- 
tinents or  on  islands  ? 

What  are  mud  volcanoes?    Solfataras? 

Earthquakes. 

What  are  earthquakes  ?  Into  what  two  classes  may  they 
be  divided  ? 

Name  some  facts  that  have  been  discovered  about  earth- 
quakes. 

Name  three  kinds  of  earthquake  motion.  Which  is  the 
most  dangerous  ? 

Describe  the  sounds  which  accompany  earthquakes. 

What  is  the  main  cause  of  earthquakes  ?  To  what  other 
causes  may  they  be  attributed? 

What  facts  have  been  discovered  respecting  the  period- 
icity of  earthquakes? 

Give  a  short  description  of  the  earthquake  which  de- 
stroyed the  city  of  Lisbon. 

Are  any  portions  of  the  earth  free  from  earthquake 
shocks  ? 

In  what  parts  of  the  earth  are  earthquake  shocks  most 
frequent  ? 

What  are  dykes  ?    How  were  they  formed  ? 

Enumerate  some  of  the  gradual  changes  of  level  which 
are  now  occurring  in  the  crust  of  the  earth.  By  what  are 
these  changes  caused  ? 


MAP  QUESTIONS. 


Trace  on  the  map  the  five  principal  volcanic  districts  of 
the  earth. 

Which  contains  the  greater  number  of  volcanoes,  the 
Atlantic  or  the  Pacific  shores  of  the  continents? 

Does  the  eastern  or  the  western  border  of  the  Indian 
Ocean  contain  the  greater  number  of  volcanoes? 

Name  the  principal  volcanic  islands  of  the  Atlantic. 
Of  the  Indian.    Of  the  Pacific. 

Locate  the  following  volcanoes :  Hecla,  Pico,  Kilauea, 
Sarmiento,  Llullayacu,  Egmont,  Cosiguina,  Teneriffe, 
Antisana,  Kilimandjaro,  Demavend,  Peshan,  Osorno,  Ere- 
bus, and  Terror. 

Name  the  principal  volcanic  mountains  of  North  America. 


In  what  part  of  the  Atlantic  Ocean  are  submarine  erup- 
tions especially  frequent  ? 

Name  three  noted  volcanoes  of  the  Mediterranean 
Sea. 

Name  the  portions  of  the  earth  which  were  shaken  by 
the  earthquake  of  Lisbon.  When  did  this  earthquake 
occur? 

What  notec"  volcanoes  are  found  in  the  region  visited  by 
the  earthquake  of  Lisbon  ? 

In  what  portions  of  the  Eastern  Hemisphere  are  earth- 
quake  shocks  especially  frequent?  In  what  portions  of 
the  Western  Hemisphere? 


" 


Section  II. 

THE  OUTSIDE  OF  THE  EARTH. 


«>X*<c 


CHAPTER   I. 
The  Crust  of  the  Earth. 

64.  Composition  of  the  Crust. — The  elementary 
substances  are  not  equally  distributed  throughout 
the  earth's  crust.  Many  of  these  substances  occur 
only  in  extremely  small  quantities,  while  others 
are  found  nearly  everywhere. 

Although  the  deepest  cutting  through  the  earth's  crust 
does  not  extend  vertically  more  than  about  two  miles  be- 
low the  level  of  the  sea,  yet  the  upturning  of  the  strata,  or 
the  outcropping  of  the  different  formations,  enables  us  to 
study  a  depth  of  about  sixteen  miles  of  the  earth's  crust. 

A  careful  study  of  the  composition  of  this  part  of  the 
crust  shows  that  oxygen  constitutes  nearly  one-half  of  it, 
by  weight.  Silicon,  an  element  which,  when  combined 
with  oxygen,  forms  silica  or  quartz,  constitutes,  either  as 
sand,  or  combined  with  various  bases  as  silicates,  one- 
fourth;  so  that  these  two  elements  form  at  least  three- 
fourths,  by  weight,  of  the  entire  crust.  The  following  are 
also  prominent  ingredients  of  rocks — aluminium,  which, 
when  combined  with  oxygen,  forms  alumina,  the  basis  of 
clay:  magnesium,  calcium,  potassium,  sodium,  iron,  and  car- 
bon. These  nine  substances,  according  to  Dana,  form 
^yVijths,  by  weight,  of  the  entire  crust. 

Sulphur,  hydrogen,  chlorine,  and  nitrogen  also  occur  fre- 
quently. The  remaining  elements  are  of  comparatively 
rare  occurrence. 

65.  The  Origin  of  Rocks. — When  the  earth  was 
yet  a  melted  globe,  the  water  which  now  covers 
the  larger  portion  of  its  surface  hung  over  it, 
uncondensed,  either  as  huge  clouds  or  as  masses 
of  vapor.  After  a  comparatively  thin  crust  had 
formed,  the  vapor  was  condensed  as  rain,  and  cov- 
ered the  earth  with  a  deep  layer  of  boiling  water. 
Occasionally  the  cooling  crust  was  broken  by  the 
increasing  tension,  and  portions  of  the  molten  in- 
terior were  forced  out  and  spread  over  the  sur- 
face. The  muddy  waters  then  cleared  by  depos- 
iting layers  of  sediment  over  the  ocean's  bed. 

When,  by  long-continued  cooling,  the  crust  be- 
came thicker,  the  breaking  out  of  the  interior  oc- 
curred less  frequently,  and  contraction,  wrinkling 
the  surface  in  huge  folds,  caused  portions  to 
emerge  from  the  ocean  and  form  dry  land.  Dur- 
ing all  this  time  the  waters  were  arranging  the 
looser  materials  in  layers  or  strata  which  were 


originally  more  or  less  horizontal;  but  wher- 
ever the  contraction  forced  the  melted  interior 
through  the  crust  or  upturned  it  in  huge  folds, 
the  horizontal  position  of  the  deposits  was  de- 
stroyed ;  and  even  when  not  so  disturbed,  the 
heat  of  the  interior,  escaping  through  fissures, 
often  produced  such  alterations  as  to  confuse  or 
completely  to  obliterate  all  traces  of  their  regu- 
lar bedding. 

The  almost  inconceivable  extent  of  geological  time  may 
be  inferred  from  the  calculations  of  Helmholtz,  based  on 
the  rapidity  of  the  cooling  of  lava.  These  calculations 
show  that  in  passing  from  a  temperature  of  2000°  C.  to 
200°  C.  a  time  equal  to  three  hundred  and  fifty  million  years 
must  have  elapsed.  Before  this  a  still  greater  time  must 
have  elapsed,  and  after  it  came  the  exceedingly  great  ex- 
tent of  geological  time  proper. 

66.  According  to  their  Origin,  rocks  may  be 
divided  into  three  distinct  classes: 

(1.)  Igneous  Rocks,  or  those  ejected  in  a  melted 
condition  from  the  interior,  and  afterward  cooled. 

(2.)  Aqueous  Rocks,  or  those  deposited  as  sedi- 
ment by  water.  When  mineral  matter  settles  in 
water,  the  coarser,  heavier  particles  reach  the  bot- 
tom first,  so  that  a  sorting  action  occurs,  which 
makes  the  different  layers  or  strata  vary  in  the 
size  and  density  of  their  particles,  and,  to  a  great 
extent,  in  their  composition. 

Aqueous  rocks  are  sometimes  called  sediment- 
ary rocks. 

(3.)  Metamorphic  Rocks,  or  those  originally 
deposited  in  layers,  but  afterward  so  changed  by 
the  a  otion  of  heat  as  to  lose  all  traces  of  stratifi- 
cation. 

This  change,  which  is  called  metamorphism,  is  caused  by 
heat  acting  under  pressure  in  the  presence  of  moisture.  Undei 
these  conditions  a  far  less  intense  heat  is  required  to  re- 
move all  traces  of  stratification.  Metamorphism  appears 
to  consist  mainly  in  a  rearrangement  of  the  chemical  con- 
stituents of  the  rocks. 

67.  According  to  their  Condition,  rocks  may 
be  divided  into  two  classes : 

(1.)  Stratified  Rocks,  or  those  arranged  in 
regular  layers.  Aqueous  rocks  are  always  strati- 
fied, and  sometimes,  though  rarely,  metamorphic 
rocks  are  stratified. 


34 


PHYSICAL    GEOGRAPHY. 


Pig.  25.    Stratified  Eock. 

In  Fig.  25  the  different  layers  or  strata  are  shown  by 
the  shadings.  Stratified  rocks  are  the  most  common  form 
of  rocks  found  near  the  earth's  surface. 

Stratified  rocks  are  largely  composed  of  fragments  of 
older  rocks;  for  this  reason  they  are  sometimes  called 
fragmental  rocks. 

(2.)  TJnstratified  Rocks,  or  those  destitute  of 
any  arrangement  in  layers.    They  are  of  two  kinds : 

(1.)  Igneous,  or  those  which  were  never  stratified. 

(2.)  Metamorphic,  or  those  which  were  once 
stratified,  but  have  lost  their  stratification  by 
the  action  of  heat. 

TJnstratified  rocks  are  sometimes  called  crystal- 
line rocks,  because  they  consist  of  crystalline 
particles. 

68.  Fossils  are  the  remains  of  animals  or  plants 
which  have  been  buried  in  the  earth  by  natural 
causes.  Generally,  the  soft  parts  of  the  organism 
have  disappeared,  leaving  only  the  harder  parts. 
Sometimes  the  soft  parts  have  been  gradually  re- 
moved, and  replaced  by  mineral  matter,  generally 
lime  or  silica;  thus  producing  what  are  called 
petrifactions.  At  times  the  mere  impression  of 
the  animal  or  plant  is  all  that  remains  to  tell 
of  its  former  existence. 


Fig.  26.    Fossil  Encrinite. 


When  the  remains  of  an  animal  or  plant  are  exposed  to 
the  air  or  buried  in  dry  earth,  they  generally  decompose 
and  pass  off  almost  entirely  as  gases;  but  when  buried 
under  water  or  in  damp  earth,  their  preservation  is  more 
probable.  Therefore,  the  species  most  likely  to  become 
fossilized  are  those  living  in  water  or  marshes,  or  in  the 
neighborhood  of  water  or  marshes. 

69.  According  to  the  Presence  or  Absence  of 
Fossil  Remains,  rocks  may  be  divided  into  two 
classes : 


(1.)  Fossiliferous  Rocks,  or  those  which  con- 
tain fossils.  They  are  stratified  and  are  of 
aqueous  origin.  Metamorphic  rocks,  in  very 
rare  instances,  are  found  to  contain  fragments 
of  fossils. 

(2.)  Non-fossiliferous  Rocks,  or  those  destitute 
of  fossils.  They  include  all  igneous  rocks  and 
most  of  those  that  are  metamorphic. 

70.  Palaeontology  is  the  science  which  treats  of  fossils. 

Palaeontology  enables  us  to  ascertain  the  earth's  condi- 
tion in  pre-historic  times,  since  by  a  careful  examination 
of  the  fossils  found  in  any  rocks  we  discover  what  animals 
and  plants  lived  on  the  earth  while  such  rocks  were  being 
deposited.  The  earth's  strata  thus  become  the  pages  of  a 
huge  book ;  and  the  fossils  found  in  them,  the  writings 
concerning  the  old  life  of  the  world.  By  their  careful 
study  geologists  have  been  enabled  to  find  out  much  of 
the  earth's  past  history. 

71.  Division  of  Geological  Time. — A  compari- 
son of  the  various  species  of  fossils  found  in  the 
earth's  crust  discloses  the  following  facts: 

(1.)  The  fossils  found  in  the  lowest  rocks  bear 
but  a  slight  resemblance  to  the  animals  and 
plants  now  living  on  the  earth. 

(2.)  The  fossils  found  in  the  intermediate  strata 
bear  a  resemblance  to  existing  species,  though 
this  resemblance  is  not  so  strongly  marked  as  in 
the  upper  strata. 

(3.)  The  fossils  found  in  the  upper  strata  bear 
a  decided  resemblance  to  existing  species. 

It  is  on  such  a  basis  that  the  immense  extent 
of  geological  time  is  divided  into  the  following 
shorter  periods  or  times: 

(1.)  Archaean  Time,  or  the  time  which  wit- 
nessed the  dawn  of  life.  This  time  included  an 
extremely  long  era,  during  most  of  which  the  con- 
ditions of  temperature  were  such  that  no  life  could 
possibly  have  existed.  Toward  its  close,  however, 
the  simplest  forms  of  life  were  created. 

The  lower  Archsean  rocks  resulted  from  the 
original  cooling  of  the  molten  earth,  and  cover 
its  entire  surface,  including  the  floor  of  the  ocean. 
On  these  rest  less  ancient  Archaean  rocks,  formed 
as  sedimentary  deposits  of  the  older  rocks. 

The  rocks  of  the  Archaean  Time  in  North  America  in- 
clude the  Laurentian,  the  lowest,  named  from  the  river 
St.  Lawrence,  near  which  they  occur,  and  the  Huronian, 
named  from  their  occurrence  near  Lake  Huron. 

(2.)  Palaeozoic  Time,  or  ancient  life,  included 
the  time  during  which  the  animals  and  plants 
bore  but  little  resemblance  to  those  now  living. 

(3.)  Mesozoic  Time,  or  middle  life,  included 
the  time  during  which  the  animals  and  plants 
began  to  resemble  those  now  living. 


THE    CRUST    OF    THE    EARTH. 


35 


(4.)  Cenozoic  Time,  or  recent  life,  included  the 
time  during  which  the  animals  and  plants  hore 
decided  resemblance  to  those  now  living. 

These  times  are  divided  into  ages. 

Archaean  Time  includes — 

(1.)  The  Azoic  Age ; 

(2.)  The  Eozoic  Age. 

Palaeozoic  Time,  or,  as  it  is  sometimes  called, 
the  Primary,  includes — 

(1.)  The  Age  of  Invertebrates,  or  the  Silurian ; 

(2.)  The  Age  of  Fishes,  or  the  Devonian ; 

(3.)  The  Age  of  Coal-plants,  or  the  Carbon- 
iferous. 

Mesozoic  Time,  or,  as  it  is  sometimes  called, 
the  Secondary,  includes  the  Age  of  Reptiles. 

Cenozoic  Time  includes — 

(1.)  The  Tertiary,  or  the  Age  of  Mammals ; 

(2.)  The  Quaternary,  or  the  Age  of  Man. 

Where  no  disturbing  causes  existed,  and  the 
land  remained  under  the  seas,  the  rocks  deposited 
during  these  periods  were  thrown  down  in  regu- 
lar strata,  one  over  the  other.  The  Archaean 
were  the  lowest ;  above  them  were  the  Palaeozoic, 
then  the  Mesozoic,  and  finally  those  of  the  Ceno- 
zoic. Generally,  however,  frequent  dislocations 
of  the  strata  have  disturbed  the  regular  order 
of  arrangement. 

72.  The  Azoic  Age  included  all  the  time  from 
the  first  formation  of  the  crust  to  the  appearance 
of  animal  and  vegetable  life. 

The  Eozoic  Age  is  that  which  witnessed  the 
dawn  of  life.  The  sedimentary  rocks  of  this  age 
are  so  highly  metamorphosed  that  nearly  all  traces 
of  life  have  been  obliterated.  Among  plants,  the 
marine  algce,  or  sea-weeds,  and  among  animals, 
the  lowest  forms  of  the  protozoa,  were  probably 
the  chief  species. 

73.  The  Age  of  Invertebrates,  or  the  Silurian, 
is  sometimes  called  the  Age  of  Mollusks.  Among 
plants,  algce,  or  sea-weeds,  are  found ;  among  ani- 
mals, protozoa,  radiates,  articulates,  and  mollusks, 
but  no  vertebrates.  Hence  the  name,  Age  of  In- 
vertebrates.    Mollusks  were  especially  numerous. 

The  name  Silurian  is  derived  from  the  ancient  Silures, 
a  tribe  formerly  inhabiting  those  parts  of  England  and 
Wales  where  the  rocks  abound. 

74.  The  Age  of  Fishes,  or  the  Devonian. — 

During  this  age  all  the  sub-kingdoms  of  animals 
are  found,  but  the  vertebrates  first  appear,  being 
represented  by  fishes,  and  from  this  fact  the  name 
has  been  given  to  the  age.  Land-plants  are  also 
found.  Immense  beds  of  limestone  and  red  sand- 
stone were  deposited. 
5 


The  name  Devonian  is  derived  from  the  district  of  Dev- 
onshire, England,  where  the  rocks  abound. 

75.  The  Age  of  Coal-Plants,  or  the  Carbonif- 
erous.— The  continents  during  this  age  consisted 
mainly  of  large,  flat,  marshy  areas,  covered  with 
luxuriant  vegetation,  subject,  at  long  intervals,  to 
extensive  inundations.  The  decaying  vegetation, 
decomposing  under  water,  retained  most  of  its 
solid  constituent,  carbon,  and  formed  beds  of  coal. 
All  the  sub-kingdoms  of  animals  were  represented 
and  reptiles  also  existed.  The  comparatively  few 
land-plants  of  the  preceding  age  now  increased 
and  formed  a  dense  vegetation. 

To  favor  such  a  luxuriant  vegetation  the  air 
must  have  been  warm  and  moist.  Since  all  the 
coal  then  deposited  previously  existed  in  the  air 
as  carbonic  acid,  the  Carboniferous  Age  was  nec- 
essarily characterized  by  a  purification  of  the 
atmosphere. 


Fig,  27.    Carboniferous  Landscape,    (A  restoration,) 

Formation  of  Coal. — In  every  100  parts  of  dry  vege- 
table matter  there  are  about  49  parts  of  carbon,  6  of  hydro- 
gen, and  45  of  oxygen.  The  carbon  is  a  solid ;  the  hydro- 
gen and  oxygen  are  gases.  It  is  from  the  carbon  that  coal 
is  mainly  formed.  When  the  decomposition  of  the  vege- 
table matter  takes  place  in  air,  the  carbon  passes  off  with 
the  hydrogen  and  oxygen  as  various  gaseous  compounds ; 
but  when  covered  by  water,  most  of  the  carbon  is  retained, 
together  with  part  of  the  oxygen  and  hydrogen.  Although 
every  year  our  forests  drop  tons  of  leaves,  no  coal  results, 
the  deposit  of  one  year  being  almost  entirely  removed 
before  that  of  the  next  occurs. 

It  has  been  computed  that  it  would  require  a  depth  of 
eight  feet  of  compact  vegetable  matter  to  form  one  foot  of 
bituminous  coal,  and  twelve  feet  of  vegetable  matter  to 
form  one  foot  of  anthracite  coal.     Anthracite  coal  differs 


36 


PHYSICAL  GEOGRAPHY. 


from  bituminous  mainly  in  the  greater  metamorphism  to 
which  it  has  been  subjected;  it  contains  a  greater  propor- 
tion of  carbon  and  less  hydrogen  and  oxygen. 

76.  The  Age  of  Reptiles. — In  this  age  the  ani- 
mals and  plants  begin  to  resemble  existing  species. 
The  age  is  characterized  mainly  by  the  prepon- 
derance of  reptiles,  many  of  which  were  very 
large,  as,  for  example,  the  plesiosaurus,  an  animal 
with  a  long,  snake-like  neck  and  a  huge  body,  or 
the  ichthyosaurus,  with  a  head  like  a  crocodile  and 
short  neck  and  large  body.  Both  of  these  ani- 
mals were  furnished  with  fin-like  paddles,  and 
lived  in  the  water.  Huge  pterodactyls,  or  bat- 
like saurians,  flew  in  the  air  or  paddled  in  the 
water.     Mammals  and  birds  also  occur. 


Fig,  28.    The  Age  of  Reptiles.    (A  restoration.) 


77.  The  Age  of  Mammals,  or  the  Tertiary  Age. 
— Mammals,  or  animals  that  suckle  their  young, 
occurred  in  great  numbers,  and,  being  the  highest 


Fig.  29.    Mastodon  giganteus.    An  Animal  of  the  Mammalian  Age 

type  of  life,  gave  the  name  to  the  age.  The  ani- 
mals and  plants  of  the  Mammalian  Age  closely 
resembled  existing  species,  though  most  of  them 
were  much  larger ;  as,  for  example,  the  dinothe- 


rium,  a  huge  animal,  with  a  trunk  like  an  ele- 
phant, but  with  downward-turned  tusks;  the 
palazotherium,  and  many  others. 

78.  The  Era  of  Man,  or  the  Quaternary  Age, 
witnessed  the  introduction  of  the  present  animals 
and  plants  and  the  creation  of  man. 

79.  Changes  Now  Occurring  in  the  Earth's 
Crust. —  Geological  time  was  characterized  by  ex- 
tensive changes,  both  in  the  kind  and  luxuriance 
of  life,  and  in  the  natute  of  its  distribution. 

The  earth  is  still  undergoing  extensive  changes, 
which  are  caused  by  the  following  agencies: 

(1.)  By  the  Winds,  which  often  carry  sand 
from  a  desert  and  distribute  it  over  fertile  plains : 
in  this  manner  the  narrow  tract  of  fertile  land  on 
the  borders  of  the  Nile,  in  Egypt,  receives  much 
sand  from  the  Sahara.  The  winds  are  also  piling 
up  huge  mounds  of  sand  along  the  sea-coasts, 
forming  what  are  called  dunes,  or  sandhills. 

(2.)  By  the  Moisture  of  the  Atmosphere,  soak- 
ing into  porous  rocks  or  running  into  the  crevices 
between  solid  ones.  This  water  in  freezing  ex- 
pands with  force  sufficient  to  rend  the  rock  into 
fragments,  which  are  carried  away  by  the  rivers 
or,  when  sufficiently  small,  by  the  winds. 

(3.)  By  the  Action  of  Running  Water. — Rivers 
wash  away  portions  of  their  banks  or  cut  their 


Fig.  30.    Curious  Effect  of  Erosion. 
way   through    their    channels.     This 


called   erosion. 


action    is 
It   occurs   even   in  the  hardest 


DISTRIBUTION    OF    THE    LAND-AREAS. 


37 


rocks.  The  materials  thus  carried  away  are 
spread  over  the  lowlands  near  the  mouth  of  the 
river  or  thrown  into  the  sea,  where  they  often 
form  large  deposits.  By  the  constant  action  of 
these  causes  the  mean  heights  of  the  continents  are 
decreasing  and  their  breadths  increasing. 

The  most  remarkable  instance  of  erosion  is 
found  in  the  canons  of  the  Colorado  River,  where 
the  waters  have  eaten  a  channel  through  the  hard 
limestones  and  granites  that  form  the  bed  of  the 
stream,  until  they  now  run  through  gorges  whose 
walls  ascend  almost  perpendicularly  to  the  height 
of  from  3000  to  6000  feet. 

A  good  idea  of  this  great  depth  may  be  obtained  by 
walking  along  a  straight  street  for  about  a  mile  (5280 
feet),  and  then  imagining  the  street  set  upright  in  the  air. 
On  looking  down  toward  the  starting- place,  we  would  see 
it  as  it  would  appear  at  the  bottom  of  a  hole  about  6000 
feet  deep. 

The  forms  produced  by  erosion  are  often  extremely  fan- 
tastic. Tall,  slender,  needle-like  columns,  capped  by  a 
layer  of  harder  rock,  sometimes  occur,  thus  showing  in  a 
marked  manner  an  effect  of  erosion. 

(4.)  By  the  Action  of  Ocean  Waves,  changing 
the  outlines  of  coasts ;  as  may  be  seen  in  portions 
of  the  coasts  of  England  and  Scotland. 

(5.)  By  the  Agency  of  Man,  witnessed  mainly 
in  the  destruction  of  the  forests  over  extended 
areas. 

(6.)  By  the  Contraction  of  a  Cooling  Crust, 
resulting  in — 1.  Earthquakes;  2.  Volcanoes;  3. 
Gradual  uplifts  and  subsidences. 


°X*c 


CHAPTER   II. 

Distribution  of  the  Land-Areas. 

80.  Geographic  Effects  of  Light,  Heat,  and 
Moisture. — The  peculiarities  observed  in  the  dis- 
tribution of  animal  and  vegetable  life  are  caused 
by  differences  in  the  distribution  of  light,  heat, 
and  moisture.  Since  light,  heat,  and  moisture 
are  influenced  by  the  interaction  of  land,  water, 
and  air,  we  must  first  study  the  distribution  and 
grouping  of  these  inorganic  or  dead  forms  before 
we  can  understand  those  that  are  living. 

81.  The  Distribution  of  the  Land.— Of  the 
197,000,000  square  miles  that  make  up  the 
earth's  surface,  about  144,000,000  are  water  and 
53,000,000  land.  The  proportion  is  about  as  the 
square  of  5  is  to  the  square  of  3.  If,  therefore, 
we  erect  a  square  on  a  side  of  five,  its  entire  area 
will  represent  the  relative  water-area  of  the  globe ; 


while  a  square  whose  side  is  three  will  represent 
the  relative  land-area. 


rr^z-r — _r^_—    - — —    -  .         — 

— — ~    ~^n 

:=—z -^=^r^^~-z5~=E:~Z^-— 

=Z-^I?^~= 

'  -r=    '144,000,000  square 

miles.  -=r-  —   — -m 

___    _    —    

_- :_: — _    : 

=    -    —=-.—     —  '  — =-  ■ ■ 

— : 

z^Ezg^fjzTi: 

"0,  Land-Area,  M 

—-z=rz= 

5:5,000,000  square  miles.        ; 

— —    - —     — 

IZzf^^yp^F 

Tig,  31.    Kelative  Land-  and  Water-Areas. 

82.  The  Distribution  of  the  Land  can  be  best 
studied  when  arranged  under  two  heads : 

(1.)  The  Horizontal  Forms  of  the  Land,  or  the 
different  shapes  produced  in  the  land-areas  by  the 
coast  lines,  or  by  the  contact  of  land  and  water ; 

(2.)  The  Vertical  Forms  of  the  Land,  produced 
by  the  irregularity  of  the  surface  of  the  high 
lands  and  low  lands. 

83.  The  Horizontal  Forms. — The  land-areas 
are  divided  into  continents  and  islands. 

The  Eastern  Hemisphere  contains  four  conti- 
nents :  Europe,  Asia,  Africa,  and  Australia.  The 
first  three  form  one  single  mass,  which  is  called 
the  Eastern  Continent. 

Though  the  word  "  continent "  strictly  refers  to  an  ex- 
tended area  of  land  entirely  surrounded  by  water,  usage 
has  sanctioned  the  application  of  the  term  to  the  grand 
divisions  of  the  land.  It  is  quite  correct,  therefore,  to 
speak  of  the  North  American  Continent,  the  Asiatic  Con- 
tinent, etc. 

T\e  Western  Hemisphere  contains  two  conti- 
nents :  North  and  South  America ;  these  consti- 
tute what  is  called  the  Western  Continent. 

The  following  are  the  extremities  of  the  conti- 
nents : 

In  the  Eastern  Continent — 

Most  northern  point,  Cape  Chelyuskin,  lat.  78°  16'  N. 

Most  southern  point,  Cape  Agulhas,  lat.  34°  51'  S. 

Most  eastern  point,  East  Cape,  long.  170°  W. 

Most  western  point,  Cape  Verd,  long.  17°  34'  W. 

In  the  Western  Continent— 

Most  northern  point,  Point  Barrow,  lat.  72°  N. 

Most  southern  point,  Cape  Froward,  lat.  53°  53'  S. 

Most  western  point,  Cape  Prince  of  Wales,  long.  168°  W. 

Most  eastern  point,  Cape  St.  Koque,  long.  35°  W. 


38 


PHYSICAL    GEOGRAPHY. 


84.  Peculiarities  in  the  Distribution  of  the 
Land: 

(1.)  The  continents  extend  farther  to  the  north 
than  to  the  south. 

(2.)  The  land  masses  are  crowded  together  near 
the  north  pole,  which  they  surround  in  the  shape 
of  an  irregular  ring. 

(3.)  The  three  main  southern  projections  of 
the  land — South  America,  Africa,  and  Australia 
— are  separated  from  each  other  by  extensive 
oceans. 

85.  Land  and  Water  Hemispheres. — The  ac- 
cumulation of  the  land  in  the  north  and  its  sepa- 
ration in  the  south  lead  to  a  curious  result — nearly 
all  the  land  is  collected  in  one  hemisphere. 

If  one  point  of  a  pair  of  compasses  be  placed  at 
the  north  pole  of  a  globe,  and  the  other  stretched 
out  to  reach  to  any  point  on  the  equator,  they 
will  describe  on  the  surface  of  the  globe  a  great 
circle,  and  consequently  will  divide  the  globe  into 
hemispheres.  If,  while  they  are  stretched  this  dis- 
tance apart,  one  of  the  points  be  placed  at  about 
the  city  of  London,  a  circle  swept  with  the  other 
point  will  divide  the  earth  into  land  and  water 
hemispheres.  Such  a  great  circle  would  pass 
through  the  Malay  Peninsula  and  the  coast  of 
Peru. 

The  Land  Hemisphere  contains  all  of  North 
America,  Europe,  and  Africa,  and  the  greater  part 
of  South  America  and  Asia.  The  Water  Hemi: 
sphere  contains  the  southern  portions  of  South 
America,  the  Malay  Peninsula,  and  Australia. 


,? 


Fig.  32.    Land  and  Water  Hemispheres. 

86.  Double  Continents. — The  six  grand  divis- 
ions or  continents  may  be  divided  into  three  pairs, 
called  Double  or  Twin  Continents. 

Each  Double  Continent  consists  of  a  northern 
and  southern  continent,  almost  separated  from 
each  other,  but  connected  by  a  narrow  isthmus 
or  island  chain. 

The  three  double  continents  are  North  and 
South   America,  Europe  and   Africa,  and  Asia 


and  Australia.    There  are,  therefore,  three  north- 
ern and  three  southern  continents. 

The  northern  continents  lie  almost  entirely  in 
temperate  latitudes,  while  the  southern  lie  mainly 
in  the  tropics* 

87.  Lines  of  Trend. — The  study  of  any  map 
of  the  world  on  a  Mercator's  projection  will  dis- 
close the  following  peculiarities  in  the  earth's 
structure : 

There  are  two  great  systems  of  courses,  trends,  or 
lines  of  direction,  along  which  the  shores  of  the  con- 
tinents, the  mountain-ranges,  the  oceanic  basins,  and 
the  island  chains  extend. 

These  trends  extend  in  a  general  north-easterly 
and  north-westerly  direction,  and  intersect  each 
other  nearly  at  right  angles. 

North-east  Trends. — A  straight  ruler  can  be  so  placed 
along  the  south-eastern  coasts  of  Greenland  and  the  south- 
eastern coasts  of  North  America  that  its  edge  will  touch 
most  of  their  shore  liues.  Its  general  direction  will  be 
north-east. 

It  can  be  similarly  placed  along  the  south-eastern  coast 
of  South  America,  the  north-western  coast  of  Africa,  and 
most  of  the  western  coast  of  Europe;  along  the  south- 
eastern coasts  of  Africa ;  the  south-eastern  coast  of  Hin- 
dostan ;  and  along  the  eastern  coast  of  Asia,  without  its 
general  direction  differing  much  from  north-east. 

North-west  Trends. — A  straight  ruler  can  be  so  placed 
as  to  touch  most  of  the  western  shores  of  North  America 
and  part  of  the  western  coast  of  South  America;  most 
of  the  western  coasts  of  Greenland,  or  the  north-eastern 
coasts  of  North  America,  and  part  of  the  western  coasts 
of  Africa.     All  tnese  courses  are  sensibly  north-west. 

If  placed  with  one  end  at  the  mouth  of  the  Mackenzie 
River,  and  the  other  on  the  south-western  extremity  of 
Lake  Michigan,  it  will  cut  nearly  all  the  great  lakes  in 
Central  British  America.  The  direction  of  the  island 
chains  of  the  Pacific  Ocean  in  particular  is  characterized 
by  these  two  trends,  many  of  the  separate  islands  being 
elongated  in  the  direction  of  the  trend  of  their  chain. 

88.  Continental  Contrasts.  —  The  main  pro~ 
longation  of  the  western  continent  extends  in  the 
line  of  the  north-western  trend,  while  that  of  the 
eastern  continent  extends  in  the  line  of  the  north- 
eastern trend.  The  axes  of  the  continents,  or 
their  lines  of  general  direction,  therefore,  inter- 
sect each  other  nearly  at  right  angles. 

The  western  continent  extends  far  north  and 
south  of  the  equator,  while  the  eastern  lies  mainly 
north  of  the  equator.  The  Western  Continent, 
therefore,  is  characterized  by  a  diversity  of  cli- 
mates; the  Eastern  Continent,  by  a  similarity. 
The  distribution  of  vegetable  and  animal  life 
in  each  continent  is  necessarily  affected  by  the 
peculiarities  of  its  climate. 

It  is  from  the  prevalence  of  the  lines  of  trend  that  the 


ISLANDS. 


39 


general  shape  of  the  continents  is  mainly  triangular.  An 
excellent  system  of  map-drawing  has  been  devised  on  this 
peculiarity. 

The  following  peculiarities  exist  in  the  coast 
lines  of  the  continents  : 

The  coast  lines  of  the  northern  continents  are 
very  irregular,  the  shores  being  deeply  indented 
with  gulfs  and  hays,  while  those  of  the  southern  con- 
tinents are  comparatively  simple  and  unbroken. 

The  continents  are  most  deeply  indented  near 
the  regions  where  the  pairs  of  northern  and  south- 
ern continents  are  nearly  separated  from  each 
other.  These  regions  correspond  with  the  lines  of 
great  volcanic  activity,  and  appear  to  be  areas  over 
which  considerable  subsidence  has  occurred. 

The  continents  differ  greatly  from  one  another 
in  their  indentations.  Europe  is  the  most  indented 
of  all  the  continents.  The  area  of  her  peninsulas, 
compared  with  that  of  her  entire  area,  is  as  1  to  4. 
Asia  comes  next  in  this  respect,  the  proportion 
being  1  to  5j,  while  in  North  America  it  is  but 
1  to  14. 

The  following  Table  gives  in  the  first  column  the  area 
of  each  of  the  continents,  in  the  second  the  length  of  coast 
line,  and  in  the  third  the  number  of  square  miles  of  area 
to  one  mile  of  coast  line : 


CONTINENTS. 


Asia 

Africa 

North  America.. 
South  America... 

Europe 

Australia 


17,500,000  sq.  miles. 

12,000,000  " 
8,400,000  " 
6,500,000  " 
3,700,000  " 
3,000,000         " 


COAST  LINE. 


35,000  miles. 
16,000  " 
22,800  " 
14,500  " 
19,500  " 
10,000     " 


Sq.  m.  of 
surface 
fori.  m. 
of  coast. 


500 
750 
368 
449 
190 
300 


Europe  has,  in  proportion  to  its  area, 

About  three  times  as  much  coast  line  as  Asia. 
About  four  times  as  much  as  Africa. 
About  twice  as  much  as  North  America. 
More  than  twice  as  much  as  South  America. 

Europe  is  the  most,  and  Africa  the  least,  deeply 
indented  of  the  continents. 


KJ^C 


CHAPTER   III. 
Islands. 

89.  Relative  Continental  and  Insular  Areas. — 

Of  the  53,000,000  square  miles  of  land,  nearly 
3,000,000,  or  about  one-seventeenth,  is  composed 
of  islands. 

90.  Varieties  of  Islands. — Islands  are  either 
continental  or  oceanic. 

Continental  Islands  are  those  that  lie  near  the 


shores  of  the  continents.  They  are  continuations 
of  the  neighboring  continental  mountain-ranges 
or  elevations,  which  they  generally  resemble  in 
geological  structure.  They  may,  therefore,  be  re- 
garded as  projections  of  submerged  portions  of  the 
neighboring  continents.  Continental  islands  have, 
in  general,  the  same  lines  of  trend  as  the  shores  of 
the  neighboring  mainland. 

Continental  islands,  as  a  rule,  are  larger  than  oceanic 
islands.  This  is  caused  by  the  shallower  water  in  which 
continental  islands  are  generally  situated.  Papua  and 
Borneo  have  each  an  area  of  about  250,000  square  miles ; 
either  of  these  islands  is  more  than  twice  as  large  as  the 
combined  areas  of  Great  Britain  and  Ireland. 

91.  American  Continental  Island  Chains. 

(1.)  The  Arctic  Archipelago  comprises  the 
large  group  of  islands  north  of  the  Dominion 
of  Canada.  It  consists  of  detached  portions  of 
the  neighboring  continent. 

(2.)  The  Islands  in  the  Gulf  of  St.  Lawrence 
and  its  neighborhood  are  apparently  the  northern 
prolongations  of  the  Appalachian  mountain-sys- 
tem. 

(3.)  The  Bahamas  lie  off  the  south-eastern  coast 
of  Florida,  to  whioh  they  belong  by  position  and 
structure.     Their  general  trend  is  north-west. 

(4.)  The  West  Indies  form  a  curved  range, 
which  connects  the  peninsula  of  Yucatan  with 
the  coast-mountains  of  Venezuela.  Here  both 
trends  appear,  though  the  north-western  pre- 
dominates. 


Fig.  33.    West  India  Island  Chain. 
1,  Cuba;  2,  Hayti;  3,  Jamaica;  4,  Porto  Rico;  5,  Caribbee  Islands; 
6,  Bahamas. 

(5.)  The  Aleutian  Islands  form  another  curved 
range,  which  connects  the  Alaskan  Peninsula  with 
Kamtchatka;  their  general  trend  is  north-east. 
They  are  connected  with  the  elevations  of  the 
North  American  continent. 


40 


PHYSICAL    GEOGRAPHY. 


(6.)  The  Islands  west  of  the  Dominion  of  Can- 
ada and  Alaska.  These  are  clearly  the  summits 
of  submerged  northern  prolongations  of  the  Pa- 
cific coast  ranges. 

(7.)  The  Islands  of  the  Patagonian  Archi- 
pelago are  the  summits  of  submerged  prolonga- 
tions of  the  Andes  of  Chili. 

92.  Asiatic  Continental  Island  Chains  consist 
of  a  series  of  curved  ranges  extending  along  the 
entire  coast,  and  intersecting  each  other  nearly  at 
right  angles. 

(1.)  The  Kurile  Islands  are  a  prolongation  of 
the  Kamtchatkan  range. 

(2.)  The  Islands  of  Japan  extend  in  a  curve 
from  Saghalien  to  Corea. 

(3.)  The  Loo  Choo  Islands  extend  in  a  curve 
from  the  islands  of  Japan  to  the  island  of  For- 
mosa. 

(4.)  The  Philippines  form  two  diverging  chains, 
which  merge  on  the  south  into  the  Australasian 
Island  chain.  The  eastern  chain  extends  to  the 
southern  extremity  of  Celebes,  and  the  western 
to  that  of  Borneo. 

The  Asiatic  chains  belong  to  a  submerged  mountain- 
range  extending  from  Kamtchatka  to  the  Sunda  Islands. 
Their  general  direction  is  parallel  to  the  elevations  of  the 
coast. 

93.  The  Australasian  Island  Chain. 

The  Australasian  Island  chain  is  composed  of 
a  number  of  islands  extending  along  curved 
trends  over  a  length  of  nearly  6000  miles,  from 
Sumatra  to  New  Zealand.  The  islands  extend 
along  three  curved  lines,  whose  general  direction 
is  north-west. 


Fig.  34.    Australasian  Island  Chain. 
1,  Sumatra ;  2,  Java ;  3,  Sumbawa  ;  4,  Flores ;  5,  Timor ;  6,  Borneo ; 
7,  Celebes;  8,  Gilolo;  9,  Ceram;   10,  Papua;  11,  Louisiade  Archipel- 
ago; 12,  New  Caledonia;  13,  New  Zealand;  14,  Admiralty  Islands; 
15,  Solomon's  Archipelago;  16,  Santa  Cruz;  17,  New  Hebrides. 


The  Australasian  chain  was  probably  connected  with  the 
Asiatic  continent  during  recent  geological  time,  and  sepa- 
rated from  it  by  subsidence.  Its  numerous  volcanoes  and 
coral  formations  prove  that  subsidence  is  still  taking 
place. 

94.  Peculiarity  of  Distribution. — The  follow- 
ing peculiarity  is  noticed  in  the  distribution  of 
continental  islands : 

Each  of  the  continents  has  an  island,  or  a  group 
of  islands,  near  its  south-eastern  extremity.  For 
example,  North  America  has  the  Bahamas  and 
the  West  Indies ;  Greenland  has  Iceland  ;  South 
America  has  the  Falkland  Islands ;  Africa  has 
Madagascar;  Asia  has  the  East  Indies;  and 
Australia  has  Tasmania. 

95.  Oceanic  Islands  are  those  situated  far  away 
from  the  continents.  They  occur  either  in  vast 
chains,  which  generally  extend  along  one  or  the 
other  of  the  two  lines  of  trend,  or  as  isolated 
groups. 

Oceanic  Island  Chains. 

The  following  are  the  most  important : 

(1.)  The  Polynesian  Chain  ; 

(2.)  The  Chain  of  the  Sandwich  Islands ; 

(3.)  The  Tongan  or  New  Zealand  Chain. 


Fig.  35.    Polynesian  Island  Chain. 
1,  Marquesas;  2,  Paumotu ;  3,  Tahitian;  4,  Rurutu  group;  5,  Her- 
vey  group;  6,  Samoan,  or  Navigator's;  7,  Vakaafo  group;  8,  Vaitupu ; 
9,  Kingsmill ;  10,  Ralick ;  11,  Radack  ;  12,  Carolines;  13,  Sandwich. 

The  Polynesian  Chain  consists  of  a  series  of 
parallel  chains,  extending  from  the  Paumotu  and 
the  Tahitian  Islands  to  the  Carolines,  the  Ralick, 
and  the  Radack  groups.  Their  general  direction 
is  north-west ;  the  total  length  of  the  chain  is 
about  5500  miles. 

The  Chain  of  the  Sandwich  Islands  extends  in 
a  north-westerly  direction.  Its  length  is  about 
2000  miles. 

The  New  Zealand  Chain  extends  north-east  as 


ISLANDS. 


41 


far  as  the  Tonga  Islands,  cutting  the  Australasian 
chain  at  right  angles. 

96.  Isolated  Oceanic  Islands  are  mainly  of  two 
kinds :  the  Volcanic  and  the  Coral.  As  a  rule,  the 
Volcanic  islands  are  high,  while  Coral  islands  sel- 
dom rise  more  than  twelve  feet  above  the  water. 

Volcanic  Islands  are  not  confined  to  isolated 
groups,  but  occur  also  in  long  chains.  The  Poly- 
nesian, Sandwich,  and  New  Zealand  Chains  con- 
tain numerous  volcanic  peaks.  But  the  high,  iso- 
lated oceanic  islands  are  almost  always  of  volcanic 
origin,  and,  consisting  of  the  summits  of  subma- 
rine volcanoes,  are  generally  small.  Some  of  the 
Canary  and  Sandwich  Islands,  which  are  of  this 
class,  rise  nearly  14,000  feet  above  the  sea. 

97.  Coral  Islands,  or  Atolls,  though  of  a  great 
variety  of  shapes,  agree  in  one  particular : 

They  consist  of  a  low,  narrow  rim  of  coral  rock, 
enclosing  a  body  of  water  called  a  lagoon. 


Fig.  36.    A  Coral  Island. 

98.  Mode  of  Formation  of  Coral  Islands. — The 

reef  forming  the  island  is  of  limestone,  derived 
from  countless  skeletons  of  minute  polyps  that 
once  lived  beneath  the  surface  of  the  waters. 
The  skeletons,  however,  are  not  separate.  The 
polyp  propagates  its  species  by  a  kind  of  bud- 
ding ;  that  is,  a  new  polyp  grows  out  of  the  body 
of  the  old.  In  this  way  the  skeletons  of  count- 
less millions  of  polyps  are  united  in  one  mass  and 
assume  a  great  variety  of  shapes. 

One  of  the  most  common  species  of  reef-forming  corals, 
the  madrepora,  is  shown  in  Fig.  37.  Many  other  forms 
exist.  i 

The  delicate  coral  structures,  together  with 
shells  from  various  shellfish,  are  ground  into  frag- 
ments by  the  action  of  the  waves,  and  by  the  in- 


Fig.  37.    Coral. 

filtration  of  water  containing  lime  in  solution, 
they  become  compacted  into  hard  limestone,  on 
which  new  coral  formations  grow. 

The  growth  of  the  coral  mass  is  directed  up- 
ward, and  ceases  when  low-water  mark  is  reached, 
because  exposure  to  a  tropical  sun  kills  the  polyps. 
But  the  action  of  the  waves  continues,  and  the 
broken  fragments  are  gradually  thrown  up  above 
the  general  level  of  the  water.  In  this  way  a  reef 
is  formed,  whose  height  is  limited  by  the  force  of 
the  waves,  and  seldom  exceeds  twelve  feet. 

On  the  bare  rock,  which  has  thus  emerged,  a 
soil  is  soon  formed  and  a  scanty  vegetation  ap- 
pears, planted  by  the  hardy  seeds  scattered  over 
it  by  the  winds  and  waves. 

The  coral  island  never  affords  a  very  comfortable  resi- 
dence for  man.  The  palm  tree  is  almost  the  only  valuable 
vegetable  species ;  the  animals  are  few  and  small,  and  the 
arable  soil  is  limited.  Moreover,  the  island  is  subject  to 
occasional  inundations  by  huge  waves  from  the  ocean. 

99.  Distribution  of  Coral  Islands.  —According 
to  Dana,  the  reef-forming  coral  polyp  is  found 
only  in  regions  where  the  winter  temperature 
of  i,b.e  waters  is  never  lower  than  68°  Fahr. 
Some  varieties,  however,  will  grow  in  colder 
water.  Coral  islands  are  confined  to  those  parts 
of  tropical  waters  where  the  depth  does  not  greatly 
exceed  100  feet,  and  xvhich  are  protected  from  cold 
ocean-currents,  from  the  influence  of  fresh  river- 
waters,  muddy  bottoms,  and  remote  from  active  vol- 
canoes, whose  occasional  submarine  action  causes 
the  death  of  the  coral  polyp.  Though  some  coral 
polyps  grow  in  quiet  water,  the  greater  part  thrive 
best  when  exposed  to  the  breakers.  The  growth  is 
therefore  more  rapid  on  the  side  toward  the  ocean 
than  on  the  side  toward  the  island. 


42 


PHYSICAL    GEOGRAPHY. 


Coral  islands  are  most  abundant  in  the  Pacific  Ocean. 
The  following  groups  contain  numerous  coral  islands : 
the  Paumotus,  the  Carolines,  the  Radack,  the  Ealick, 
and  the  Kingsmill  groups,  and  the  Tahitiau,  Samoan, 
and  Feejee  Islands,  and  New  Caledonia. 

In  the  Indian  Ocean  the  Laccadives  and  the  Maldives  are 
most  noted. 

In  the  Atlantic  Ocean  the  West  Indies  and  the  Bermudas 
are  examples. 

100.  Varieties  of  Coral  Formations. — There 
are  four  varieties  of  coral  formations  : 

(1.)  Fringing  Reefs,  or  narrow  ribbons  of  coral 
rock,  lying  near  the  shore  of  an  ordinary  island. 

(2.)  Barrier  Beefs,  which  are  broader  than 
Fringing  Reefs,  and  lie  at  a  greater  distance 
from  the  shore,  but  do  not  extend  entirely  around 
the  island. 

A  barrier  reef  off  the  coast  of  New  Caledonia  has  a 
length  of  400  miles.  One  extends  along  the  north-eastern 
shore  of  Australia  for  over  1000  miles.  Barrier  reefs  are 
not  continuous,  but  often  have  breaks  in  them  through 
which  vessels  can  readily  pass. 

(3.)  Encircling  Reefs  are  barrier  reefs  extend- 
ing entirely  around  the  island.  As  a  rule,  en- 
circling reefs  are  farther  from  the  shores  of  the 
island  than  barrier  reefs.  Tahiti,  of  the  Society 
Islands,  is  an  example  of  an  encircling  reef. 

(4.)  Atolls. — This  name  is  given  to  reefs  that 
encircle  lagoons  or  bodies  of  water  entirely  free 
from  islands. 

The  varieties  of  reefs  just  enumerated  mark 
successive  steps  or  stages  in  the  progress  of  for- 
mation of  the  coral  island. 

When  a  more  careful  study  of  the  habits  of  the  reef- 
forming  coral  polyp  disclosed  the  fact  of  its  inability  to 
live  in  the  ocean  at  greater  depths  than  100  or  120  feet, 
the  opinion,  which  formerly  prevailed,  of  coral  islands 
rising  from  profound  depths,  had  to  be  abandoned.  The 
idea  had  its  foundation  in  the  fact  that  a  sounding-line, 
thrown  into  the  water  near  the  shore  of  a  coral  island, 
almost  invariably  showed  depths  of  thousands  of  feet,  and 
yet  brought  up  coral  rock.  In  no  case,  however,  did  the 
rock  contain  living  polyps.  An  ingenious  hypothesis  of 
Darwin,  which  appears  well  sustained  by  the  extensive 
observations  of  Dana  and  others,  explains  the  great  depth 
of  coral  formations. 

101.  Darwin's  Theory  of  Coral  Islands. — Ac- 
cording to  this  distinguished  naturalist,  the  coral 
formation  begins  near  the  shore  of  an  island  that 
is  slowly  sinking.  If  the  growth  of  the  reef  up- 
ward equals  the  sinking  of  the  island,  the  thick- 
ness of  the  reef  is  limited  only  by  the  time  during 
which  the  operation  continues. 

In  Fig.  38  is  shown,  in  plan  and  section,  an  island  with 
elevations  A,  and  B,  and  river  a.  The  coral  island  begins 
as  a  fringing  reef  somewhere  off  the  coast  of  an  ordinary 
island  at  c,  c,  c,  when  the  conditions  are  favorable.     The 


Fig,  38.    Growth  of  a  Coral  Island. 

coral  reef  must  gradually  extend  around  the  island,  since  its 
growth  toward  the  ocean  is  soon  limited  by  the  increasing 
depth,  and  toward  the  shore  of  the  island  by  the  muddy 
waters  near  the  surf  and  the  absence  of  the  breakers. 

Meanwhile,  as  the  island  is  sinking,  the  channel  sepa- 
rating the  reef  from  the  coast  increases  in  breadth.  A 
barrier  reef  is  thus  formed,  which  at  last  completely  sur- 
rounds the  island,  and  becomes  an  encircling  reef.  The 
higher  portions  of  land,  which  are  still  above  the  waters, 
form  islands  in  the  central  lagoon.  Opposite  the  mouth 
of  the  river  a,  the  growth  is  prevented  by  the  fresh  water, 
and  a  break  in  the  reef  is  thus  produced.  These  breaks 
are  sometimes  sufficient  to  permit  a  ship  to  enter  the 
lagoon.  At  last  all  traces  of  the  old  island  disappear,  and 
its  situation  is  marked  by  a  clear  lake,  surrounded  by  a 
narrow  rim  of  coral  which  follows  nearly  the  old  coast 
line. 

A  coral  island,  therefore,  is  always  of  an  ap- 
proximately circular  or  oval  form,  and  encloses  a 
clear  space  in  the  ocean.  Extended  systems  of  coral 
formations  occurring  in  any  region  are  a  proof  of 
subsidence. 


CHAPTER   IV. 

Relief  Forms  of  the  Land. 

102.  By  the  Forms  of  Relief  of  the  Land  is 

meant  the  elevation  of  the  land  above  the  mean 
level  of  the  sea. 

The  highest  land  in  the  world  is  Mount  Ever- 
est, of  the  Himalayas;  it  is  29,000  feet  high. 
The  greatest  depression  is  the  Dead  Sea,  in  Pales- 
tine, which  is  about  1312  feet  below  the  level  of 
the  ocean.  The  sum  of  these  is  somewhat  less 
than  six  miles. 

An  elevation  of  six  miles  is  insignificant  when 


RELIEF  FORMS  OF  THE  LAND. 


43 


compared  with  the  size  of  the  earth.  If  repre- 
sented on  an  ordinary  terrestrial  globe,  it  would 
be  scarcely  discernible,  since  it  would  project 
above  the  surface  only  about  the  y^Vifth  0I>  the 
diameter.  The  highest  elevations  of  the  earth  are 
proportionally  much  smaller  than  the  wrinkles  on 
the  skin  of  an  orange. 


Fig,  39,    Eelative  Height  of  Mountains. 

If,  as  in  Fig.  39,  a  sphere  be  drawn  to  represent  the  size 
of  the  earth,  its  radius  will  be  equal  to  about  4000  miles. 
If,  now,  the  line  A  B  be  drawn  equal  to  the  radius,  it 
will  represent  a  height  of  4000  miles.  One-half  this 
height  would  be  2000  miles;  one-half  of  this  1000,  and 
successive  halves  500  and  250  miles.  An  elevation  of  250 
miles  would  not  therefore  be  very  marked. 

Although  the  irregularities  of  the  surface  are 
comparatively  insignificant,  they  powerfully  affect 
the  distribution  of  heat  and  moisture,  and  conse- 
quently that  of  animal  and  vegetable  life.  An 
elevation  of  about  350  feet  reduces  the  tempera- 
ture of  the  air  1°  Fahr. — an  effect  equal  to  a 
difference  of  about  70  miles  of  latitude.  High 
mountains,  therefore,  though  under  the  tropics, 
may  support  on  their  higher  slopes  a  life  similar 
to  that  of  the  temperate  and  the  polar  regions. 

103.  The  Relief  Forms  of  the  Land  are  divided 
into  two  classes : 

Low  Lands  and  High  Lands. 

The  boundary-line  between  them  is  taken  at 
1000  feet,  which  is  the  mean  or  average  elevation 
of  the  land. 

Low  Lands  are  divided  into  plains  and  hills. 

High  Lands  are  divided  into  plateaus  and 
mountains. 

If  the  surface  is  comparatively  flat  or  level,  it 
is  called  a  plain  when  its  elevation  above  the  sea 
is  less  than  1000  feet,  and  a  plateau  when  its  ele- 
vation is  1000  feet  or  over. 
6 


If  the  surface  is  diversified,  the  elevations  are 
called  hills  when  less  than  1000  feet  high ;  and 
mountains  when  1000  feet  or  over. 

104.  Plains  and  Hills  cover  about  one-half  of 
the  land  surface  of  the  earth.  In  the  Eastern 
Continent  they  lie  mainly  in  the  north;  in  the 
Western,  they  occupy  the  central  portions. 

Plains  generally  owe  their  comparatively  level 
surface  to  the  absence  of  wrinkles  or  folds  in  the 
crust,  in  which  case  the  general  level  is  preserved, 
but  the  surface  rises  and  falls  in  long  undulations : 
these  may  therefore  be  called  undulating  plains. 

The  flat  surface  may  also  be  due  to  the  gradual 
settling  of  sedimentary  matter.  In  this  case  the 
plains  are  exceedingly  level.  They  are  called 
marine  when  deposited  at  the  bottom  of  a  sea  or 
ocean,  and  alluvial  when  deposited  by  the  fresh 
water  of  a  river  or  lake.  Alluvial  plains  occur 
along  the  lower  course  of  the  river  or  near  its 
mouth. 

Marine  and  alluvial  plains,  from  their  mode  of  forma- 
tion, are  generally  less  elevated  than  undulating  plains. 

105.  Plateaus  are  generally  found  associated 
with  the  mountain-ranges  of  the  continents.  Their 
connection  with  the  adjacent  plains  is  either  ab- 
rupt, as  where  the  plateau  of  Anahuac  joins  the 
low  plains  on  the  Mexican  Gulf;  or  gradual,  as 
where  the  plains  of  the  Mississippi  Valley  join 
the  plateaus  east  of  the  Rocky  Mountains. 

106.  Mountains.  —  In  a  mountain-chain  the 
crest  or  summit  of  the  range  separates  into  a  num- 
ber of  detached  portions  called  peaks;  below  the 
peaks  the  entire  range  is  united  in  a  solid  mass. 

The  breaks  in  the  ridge,  when  extensive,  form 
mountain-passes. 

The  influence  of  inaccessible  mountains,  like  the  Pyr- 
enees and  Himalayas,  in  preventing  the  intermingling  of 
nations  living  on  their  opposite  sides,  is  well  exemplified 
by  history.  In  the  past,  mountains  formed  the  boundaries 
of  different  races.  Some  mountains,  like  the  Alps  and  the 
Appalachians,  have  numerous  passes. 

A  Mountain-System  is  a  name  given  to  several 
connected  chains  or  ranges.  Mountain-systems 
are  often  thousands  of  miles  in  length  and  hun- 
dreds of  miles  in  breadth. 

The  Axis  of  a  Mountain-system  is  a  line  extend- 
ing in  the  general  trend  of  its  chains. 

Where  several  mountain-axes  intersect  one  an- 
other, a  complicated  form  occurs,  called  a  Moun- 
tain-Knot. 

The  Pamir  Knot,  formed  by  the  intersection  of  the 
Karakorum,  Belor,  and  Hindoo-Koosh  Mountains,  is  an 
example.  It  lies  on  the  southern  border  of  the  elevated 
plateau  of  Pamir. 


44 


PHYSICAL    GEOGRAPHY. 


A  Mountain-Pass, 

mountains   and   their 


Fig.  40 

107.  Orology  treats  of 
formation. 

The  force  which  upheaved  the  crust  into  moun- 
tain-masses and  plateaus  had  its  origin  in  the 
contraction  of  a  cooling  globe.  There  are  good 
reasons  for  believing  that  no  extensive  mountains 
existed  during  the  earlier  geological  ages,  since 
the  crust  was  then  very  thin,  and  would  have 
been  fractured  before  sufficient  force  could  accu- 
mulate to  upheave  it  into  mountain-masses. 

The  great  mountain-systems  of  the  world  are 
formed  from  sedimentary  deposits  that  slowly  ac- 
cumulated over  extended  areas  until  they  acquired 
very  great  thickness.  The  deposits  forming  the 
Appalachians,  according  to  Dana,  were,  in  places, 
40,000  feet  in  depth,  and  covered  the  eastern  bor- 
der of  the  continent  from  New  York  to  Alabama, 
varying  from  100  to  200  miles  in  breadth. 

After  the  accumulation  of  these  strata  they 
were,  through  the  contraction  of  the  crust,  sub- 
jected to  the  gradual  effects  of  lateral  pressure, 
by  which  they  were  sometimes  merely  flexed  or 
folded,  but  more  frequently  crushed,  fractured,  or 
mashed  together,  and  thus  thickened  and  thrust 
upward.  That  side  of  the  deposit  from  which 
the  thrust  came  would  have  a  steeper  slope  than 
the  opposite  side,  which  received  a  thrust  arising 
from  the  resistance. 


This  theory  of  mountain-formation,  which  is 
generally  accepted,  explains  the  following  facts : 

(1.)  All  mountains  have  two  slopes — a  short 
steep  slope,  facing  the  ocean,  and  a  long  gentle 
slope,  facing  the  interior  of  the  continent. 

(2.)  The  strata  on  the  short  steep  slope  are 
generally  highly  metamorphosed;  those  on  the 
long  slope  are  in  general  only  partially  metamor- 
phosed, or  wholly  unchanged. 

(3.)  The  mountain-systems  are  situated  on  the 
borders  of  the  continents  where  the  sedimentary 
strata  collected. 

(4.)  Slaty  cleavage,  or  the  readiness  with  which 
so  many  of  the  rocks  of  mountains  cleave  or  split 
in  one  direction,  is  a  proof  of  these  rocks  having 
been  subjected  to  intense,  long-acting,  lateral  pres- 
sure, since  such  pressure  can  be  made  to  develop 
slaty  cleavage  in  plastic  material. 

Isolated  Mountains.— Nearly  all  high  isolated  moun- 
tains were  formed  by  the  ejection  of  igneous  rocks  from 
the  interior ;  that  is,  they  are  of  volcanic  origin  and  have 
been  upheaved  by  a  vertical  strain  or  true  projectile  force, 
as  in  the  volcanic  range  of  Jorullo  in  Mexico. 

108.  Valleys  in  mountainous  regions  are  either 
longitudinal  or  transverse. 

Longitudinal  Valleys  are  those  that  extend  in 
the  direction  of  the  length  of  the  mountains. 

Transverse  Valleys  extend  across  the  moun- 
tain. It  is  in  transverse  valleys  that  most  passes 
occur. 

Although  valleys,  like  mountains,  owe  their  origin  to 
the  contraction  of  a  cooling  crust,  yet  their  present  shapes 
are  modified  by  the  operation  of  other  forces.  By  the 
action  of  their  water-courses,  valleys  are  deepened  in  one 
place  and  filled  up  in  another.  Extensive  land-slides  often 
alter  their  configuration.  During  the  Glacial  Period  many 
valleys  were  greatly  changed  by  the  action  of  huge  mov- 
ing masses  of  ice.  Fiord-valleys  were  formed  in  this 
manner. 

In  level  countries  valleys  generally  owe  their 
origin  to  the  eroding  power  of  water. 

109.  Peculiarities  of  Continental  Reliefs. — 
The  following  peculiarities  are  noticeable  in  the 
relief  forms  of  the  continents : 

(1.)  The  continents  have,  in  general,  high  bor- 
ders and  a  low  interior. 

(2.)  The  highest  border  lies  nearest  the  deep- 
est ocean;  hence,  the  culminating  point,  or  the 
highest  point  of  land,  lies  out  of  the  centre  of  the 
continent. 

(3.)  The  greatest  prolongation  of  a  continent 
is  always  that  of  its  predominant  mountain-sys- 
tem. 

(4.)   The  prevailing   trends   of   the  mountain- 


RELIEF  FORMS  OF  THE  CONTINENTS. 


45 


masses  are  the  same  as  those  of  the  coast  lines,  and 
are,  in  general,  either  north-east  or  north-west. 

In  describing  the  relief  forms  of  the  continents 
we  shall  observe  the  following  order : 

(1.)  The  Predominant  System,  or  a  system  of 


elevations  exceeding  all  others  in  height,  and  con- 
taining the  culminating  point  of  the  continent. 

(2.)  The  Secondary  System  or  Systems,  inferior 
to  the  preceding  in  height. 

(3.)  The  Great  Low  Plains. 


Fig,  41.    Orographic  Chart  of  North  America.    (Light  portions,  mountains ;  shaded  portions,  plains.) 
1,  Rocky  Mountain  System;  2,  System  of  the  Sierra  Nevada  and  Cascade  Ranges;  3,  Sierra  Madre;  4,  Great  Interior  Plateau;  5,  Wahsatch 
Mountains;  6,  Appalachians;  7,  Plateau  of  Labrador;   8,  Height  of  Land;  9,  Arctic  Plateau;   10,  Mackenzie  River;   11,  Nelson  River;  12,  St. 
Lawrence  River;  13,  Mississippi  River. 


CHAPTER  V. 

Relief  Forms  of  the  Continents. 

I.     NORTH    AMERICA 

110.  Surface  Structure.  —  The  Predominant 
Mountain-System  lies  in  the  west. 

The  Secondary  Systems  lie  in  the  east  and  north. 
The  Great  Low  Plains  lie  in  the  centre. 

111.  The  Pacific  Mountain-System,  the  pre- 
dominant system,  extends,  in  the  direction  of  the 
greatest  prolongation  of  the  continent,  from  the 
Isthmus  of  Panama  to  the  Arctic  Ocean.  It  con- 
sists of  an  immense  plateau,  from  300  to  600 
miles  in  breadth,  crossed  by  two  nearly  parallel 
mountain-systems :  the  Rocky  Mountains  on  the 
east  and  the  system  of  the  Sierra  Nevada  and 
Cascade  ranges  on  the  west.  The  eastern  moun- 
tain-system is  highest  near  the  south ;  the  west- 
ern range  is  highest  near  the  north.  Between 
these  lie  numerous  parallel  ranges  enclosing  lon- 


gitudinal valleys,  connected  in  places  by  trans- 
verse ranges  forming  basin-shaped  valleys. 

The  Rocky  Mountain  System.  —  The  Rocky 
Mountains  rise  from  the  summits  of  a  plateau 
whose  elevation,  in  the  widest  part  of  the  system, 
varies  from  6000  to  7000  feet  above  the  sea; 
therefore,  although  the  highest  peaks  range  from 
11,000  to  nearly  15,000  feet,  their  elevation  above 
the  general  level  of  the  plateau  is  comparatively 
inconsiderable.  The  plateau  on  the  east  rises  by 
almost  imperceptible  slopes  from  the  Mississippi 
River.  The  upper  parts  of  the  slopes,  near  the 
base  of  the  mountains,  form  an  elevated  plateau 
called  the  "  Plains,"  over  which,  at  one  time, 
roamed  vast  herds  of  buffalo  or  bison.  This  ani- 
mal is  rapidly  becoming  extinct. 

Though  the  name  "  Eocky  Mountains  "  is  generally  con- 
fined to  those  parts  of  the  chain  which  extend  through 
British  America  and  the  United  States,  yet,  in  connection 
with  the  Sierra  Nevada  Mountains,  it  is  continued  through 
Mexico  by  the  Sierra  Madre  Mountains,  and  by  smaller 
ranges  to  the  Isthmus  of  Panama. 


46 


PHYSICAL    GEOGRAPHY. 


Pig.  42.    On  the  Plains. 

The  Rocky  Mountain  System  forms  the  great 
watershed  of  the  continent,  the  eastern  slopes 
draining  mainly  through  the  Mississippi  into  the 
Atlantic,  and  the  western  slopes  draining  through 
the  Columbia  and  the  Colorado  into  the  Pacific. 
It  slopes  gradually  upward  from  the  Arctic  Ocean 
toward  the  Mexican  plateau,  where  it  attains  its 
greatest  elevation  in  the  volcanic  peak  of  Popo- 
catepetl, 17,720  feet  above  the  sea. 

The  System  of  the  Sierra  Nevada  and  Cascade 
Mountains  extends,  in  general,  parallel  to  the 
Rocky  Mountain  System.  It  takes  th(  name  of 
Sierra  Nevada  in  California  and  Nevada,  and  of 
the  Cascade  Mountains  in  the  remaining  portions 
of  the  continent.  It  reaches  its  greatest  eleva- 
tion in  Mount  St.  Elias,  in  Alaska,  19,500  feet 
above  the  sea.  This  is  the  culminating  point  of 
the  North  American  continent. 

In  the  broadest  part  of  the  plateau  of  the  Pacific  system, 
between  the  Wahsatch  Mountains  on  the  east,  and  the 
Sierra  Nevada  and  Cascade  ranges  on  the  west,  lies  the 
plateau  of  the  Great  Basin.  Its  high  mountain  borders 
rob  the  winds  of  their  moisture,  and  the  rainfall,  except 
on  the  mountain-slopes,  is  inconsiderable.  The  Great 
Basin  has  a  true  inland  drainage. 

The  heights  of  all  mountains,  except  those  much  fre- 
quented, must  generally  be  regarded  as  but  good  approxi- 
mations, since  the  methods  employed  for  estimating  heights 
require  ■  great  precautions  to  secure  trustworthy  results. 
Even  the  culminating  points  of  all  the  continents  have 
not,  as  yet,  been  accurately  ascertained. 

112.  The  Secondary  Mountain-Systems  of  North 
America  comprise  the  Appalachian  system,  the 


Plateau  of  Labrador,  the  Height  of  Land,  and 
the  Arctic  Plateau.  The  last  three  have  but  an 
inconsiderable  elevation. 

The  Appalachian  Mountain  System  consists  of 
a  number  of  nearly  parallel  chains  extending 
from  the  St.  Lawrence  to  Alabama  and  Georgia. 
It  is  high  at  the  northern  and  southern  ends,  and 
slopes  gradually  toward  the  middle.  The  highest 
peaks  at  either  end  have  an  elevation  of  about 
6000  feet. 

The  Appalachian  system  is  broken  by  two  deep  depres- 
sions, traversed  by  the  Hudson  and  Mohawk  Rivers.  Be- 
tween the  foot  of  the  system  and  the  ocean  lies  a  low  coast 
plain,  whose  width  varies  from  50  to  250  miles. 

113.  The  Great  Low  Plain  of  North  America 
lies  between  the  Atlantic  system  on  the  east  and 
the  Pacific  system  on  the  west.  It  stretches  from 
the  Arctic  Ocean  to  the  Gulf  of  Mexico. 

Near  the  middle  of  the  plain  the  inconsider- 
able elevation  of  the  Height  of  Land  divides  it 
into  two  gentle  slopes,  which  descend  toward  the 
Arctic  Ocean  and  the  Gulf  of  Mexico.  A  gen- 
tle swell  extending  from  north-west  to  south-east 
divides  the  northern  portion  of  the  plain  into 
two  parts.  The  eastern  and  western  basins,  so 
formed,  are  connected  by  a  break  in  the  water- 
shed, through  which  the  Nelson  River  empties 
into  Hudson  Bay. 

The  southern  part  of  the  plain  is  traversed,  in 
its  lowest  parts,  by  the  Mississippi  River. 

The  tributaries  of  this  river  descend  the  long,  gentle 
slopes  of  the  Atlantic  and  Pacific  systems. 

114.  The  Relief  Forms  of  a  Continent  are  best 
understood  by  ideal  sections,  in  which  the  base 
line  represents  the  sea-level,  and  the  scale  of 
heights  on  the  margin  represents  the  elevation 
of  the  various  parts. 

In  all  such  sections  the  vertical  dimensions  of  the  land 
are  necessarily  greatly  exaggerated. 


Fig.  43.    Section  of  North  America  from  East  to  West. 
1,  St.  Elias;  2,  Sierra  Nevada;  3,  Rocky  Mountains;  4,  Mississippi 
Valley ;  5,  Appalachian  System. 

115.  Approximate  Dimensions  of  North  America. 

Area  of  continent,  8,400,000  square  miles. 

Greatest  breadth  from  east  to  west,  about  3100  miles. 

Greatest  length  from  north  to  south,  about  4500  miles. 

Coast  line,  22,800  miles. 

Culminating  point,  Mount  St.  Elias,  19,500  feet. 


BELIEF    FORMS    OF    THE    CONTINENTS. 


4? 


Fig,  44.    Orographic  Chart  of  South  America. 
(Light  portions,  mountains ;  shaded  portions,  plains.) 
1,  System  of  the  Andes;  2,  Plateau  of  Quito;  3,  Plateau  of  Bolivia; 
4,  Aconcagua;  5,  Plateau   of  Guiana;   6,  Plateau   of  Brazil;  7,  The 
Orinoco ;  8,  The  Amazon ;  9,  The  La  Platte. 

II.     SOUTH    AMERICA. 

116.  Surface  Structure.  —  The  Predominant 
Mountain-System  of  South  America  is  in  the  west. 

The  Secondary  Systems  are  in  the  east. 
The  Great  Low  Plain  lies  between  them. 

117.  The  System  of  the  Andes,  which  extends 
along  the  western  border  of  the  continent,  is  the 
predominant  mountain-system.  It  is  composed 
mainly  of  two  approximately  parallel  chains 
separated  by  wide  and  comparatively  level  val- 
leys. On  the  north  there  are  three  chains,  and 
on  the  south  but  one ;  in  the  centre,  mainly  two. 
The  chains  are  connected  by  transverse  ridges, 
forming  numerous  mountain-knots. 

The  Andes  System  forms  a  continuation  of 
the  Pacific  Mountain-System.  A  wide  depression 
at  the  Isthmus  of  Panama  marks  their  separation. 
From  this  point  the  Andes  increase  in  height 
toward  the  south,  probably  reaching  their  high- 
est point  in  Chili,  where  the  volcanic  peak  of 
Aconcagua,  23,910  feet,  is  believed  to  be  the  cul- 
minating point  of  South  America,  and  of  the  West- 
ern Continent. 

Nevada  de  So  rata  was  formerly  believed  to  be  the  cul- 
minating point  of  South  America,  but  recent  recalculations 


of  the  observations  have  resulted  in  a  loss  of  nearly  4000 
feet  of  the  supposed  height  of  Sorata.  Some  authorities 
still  claim  that  several  peaks  in  Bolivia  reach  an  ele- 
vation of  nearly  25,000  feet. 

The  Andes  Mountain-System  terminates  ab- 
ruptly in  the  precipitous  elevations  of  Cape  Horn. 

Numerous  table-lands  are  included  between  the  parallel 
ranges :  the  most  important  are— the  plateau  of  Quito,  9543 
feet;  the  plateau  of  Pasco,  in  North  Peru,  11,000  feet;  the 
plateau  of  Bolivia,  from  12,000  to  14,000  feet.  From  most 
of  these  higher  plateaus  volcanic  peaks  arise. 

118.  The  Secondary  Mountain-Systems  of  South 
America  are  the  plateaus  of  Brazil  and  Guiana. 
They  both  lie  on  the  eastern  border. 

The  Plateau  of  Brazil  is  a  table-land  whose 
average  height  is  about  2500  feet.  Narrow 
chains  or  ridges  separate  the  river-valleys.     , 

The  plateau  of  Brazil  forms  the  watershed  between  the 
tributaries  of  the  Amazon  and  the  La  Plata.  Along  the 
Atlantic  a  moderately  continuous  range  descends  in  steep 
terraces  to  the  ocean.  The  average  altitude  is  more  than 
double  that  of  the  western  portion  of  the  plateau.  The 
highest  peaks  are  somewhat  over  8000  feet. 

The  Plateau  of  Guiana,  smaller  than  the  Plateau 
of  Brazil,  but  about  equally  elevated,  forms  the 
watershed  between  the  Orinoco  and  the  Amazon. 


Fig.  45.    Amazon  River  Scenery. 

119.  The  Great  Low  Plain  of  South  America 
lies  between  the  predominant  and  the  secondary 
mountain-systems.  It  is  mainly  of  alluvial  origin, 
but  slightly  elevated,  and  is  much  more  level  than 
the  great  plain  of  North  America. 

This  plain  is  drained  by  the  three  principal  river-sys- 


48 


PHYSICAL    GEOGRAPHY. 


terns  of  the  continent,  by  which  it  is  divided  into  three 
parts :  the  Llanos  of  the  Orinoco,  the  Selvas  of  the  Amazon, 
and  the  Pampas  of  the  La  Platte. 

The  Llanos  are  grassy  plains  which,  during  the  rainy 
season,  resemble  our  prairies,  but  during  the  dry  weather 
are  deserts. 

The  Selvas,  or  forest  plains,  are  covered  by  an  uninter- 
rupted luxuriant  forest.  The  vegetation  here  is  so  dense 
that  in  some  places  the  broad  rivers  form  the  only  ready 
means  of  crossing  the  country.  Near  the  river-banks  are 
vast  stretches  of  swampy  ground. 

The  Pampas  are  grassy  plains  which  in  some  respects 
resemble  the  Llanos. 

A  coast  plain  lies  between  the  Andes  and  the 
Pacific.     It  is  widest  near  the  Andes  of  Chili, 


Fig,  46.    Section  of  South  America  from  East  to  West, 
1,  Volcano  Arequipa;  2,  Lake  Titicaca;  3,  Nevada  de  Sorata;  4, 
Central  Plain  ;  5,  Mountains  of  Brazil. 

where  in  some  places  it  is  100  miles  in  breadth. 
Between  the  parallels  of  27°  and  23°  the  plain 


is  an  absolute  desert,  called  the  Desert  of  Ata- 
cama.  Here  rain  never  falls  and  vegetation  is 
entirely  absent. 

120.  Approximate  Dimensions  of  South  America. 
Area  of  continent,  about  6,500,000  square  miles. 
Greatest  breadth  from  east  to  west,  3230  miles. 
Greatest  length  from  north  to  south,  4800  miles. 
Coast  line,  14,500  miles. 
Culminating  point,  Aconcagua,  23,910  feet. 

121.  Contrasts  of  the  Americas. — In  both  North 
and  South  America  the  predominant  system  lies  in 
the  west,  the  secondary  systems  in  the  east,  and  the 
low  plains  in  the  centre. 

They  differ  in  the  following  respects : 

In  North  America  the  predominant  system  is  a 
broad  plateau,  having  high  mountain-ranges ;  the 
principal  secondary  system  is  narrow,  and  formed 
of  parallel  ranges ;  the  low  plains  are  character- 
ized by  undulations,  and  contain  several  deep  de- 
pressions occupied  by  extensive  lake-systems. 

In  South  America  the  predominant  system  is  nar- 
row; the  secondary  systems  are  broad ;  the  low  plain 
is  alluvial,  extremely  flat,  contains  no  depressions, 
and  consequently  no  extensive  lake-systems. 


Fig,  47,    Orographic  Chart  of  Europe.    (Light  portions,  mountains ;  shaded  portions,  plains.) 
1,  The  Alps;  2,  Mont  Blanc;  3,  Pyrenees;  4,  Cantabrian;  5,   Sierra  Estrella;   6,    Sierra  Nevada;  7,   Mountains  of  Castile;   8,  Apennines; 
9,  Dinaric  Alps;  10,  Balkan;  11,  Pihdus;  12,  Taurus;  13,  Caucasus;   14,  Cevennes;  15,  Plateau  of  Auvergne;  16,  Vosges;  17,  Black  Forest;  18, 
Jura;  19,  Hartz;  20,  Bohemian  Plateau;  21,  Carpathians;  22,  Hungarian  Forest;  23,  Transylvanian  Mountains;  24,  Kiolen  Mountains;  25,  Urals. 


III.     EUROPE. 
122.   Surface    Structure.  —  The    Predominant 
Mountain-System  is  in  the  south. 

The  Secondary  Systems  are  in  the  north  and  east. 


The  Great  Low  Plain  lies  between  the  Pre- 
dominant and  Secondary  Systems. 

A  line  drawn  from  the  Sea  of  Azov  to  the  mouth  of  the 
Rhine  Eiver  divides  Europe  into  two  distinct  physical 


regions.  The  great  low  plain  lies  on  the  north,  and  the 
predominant  mountain-system  on  the  south.  The  coun- 
try north  of  this  line  is  sometimes  called  Low  Europe,  and 
that  south  of  it,  High  Europe. 

123.  The  Predominant  Mountain-System  of  Eu- 
rope is  composed  of  a  highly  complex  series  of 
mountain-systems  extending  along  the  northern 
shores  of  the  Mediterranean  in  a  curve,  from  the 
Straits  of  Gibraltar  to  the  shores  of  Asia  Minor. 
The  system  is  highest  in  the  centre,  where  the 
Alps  form  the  culminating  point  of  the  continent. 

The  average  elevation  of  the  Alps  ranges  from 
10,000  to  12,000  feet.  The  highest  peak,  Mont 
Blanc,  15,787  feet,  is  the  culminating  point  of  the 
European  continent.  Matterhorn  and  Monte  Rosa 
are  but  little  inferior  in  height.  On  the  south- 
west the  system  is  continued  to  the  Atlantic  by 
the  Cevennes  and  adjoining  ranges  in  France,  and 
the  Pyrenees  and  Cantabrian  in  the  northern  part 
of  the  Spanish  peninsula.  The  Pyrenees  are  an 
elevated  range,  with  peaks  over  11,000  feet  high. 
On  the  east  the  system  extends  in  two  curves  to 
the  Black  Sea  by  the  Carpathian  and  Transylva- 
nian  Mountains  on  the  north,  and  the  Dinaric 
Alps  and  the  Balkan  Mountains  on  the  south. 

124.  Divisions  of  Predominant  System. — The 
predominant  mountain-system  of  Europe  may  be 
conveniently  regarded  as  consisting  of  a  central 
body  or  axis,  the  Alps,  with  six  projections  or 
limbs — three  on  the  north,  and  three  on  the  south. 

The  three  divisions  on  the  north  include — 

The  Western  Division,  or  the  mountains  of 
France,  including  the  mountains  lying  west  of 
the  valleys  of  the  Rhine  and  the  Rhone ; 

The  Central  Division,  or  the  mountains  of  Ger- 
many, situated  between  the  Western  Division  and 
the  upper  valleys  of  the  Oder  and  the  Danube ; 

The  Eastern  Division,  or  the  mountains  of 
Austria-Hungary,  situated  between  the  Central 
Division  and  the  Black  Sea. 

These  divisions  contain  a  highly  complicated  system  of 
minor  elevations.  Their  complexity  is  due  to  the  fre- 
quent intersection  of  the  north-eastern  and  north-western 
trends.  Basin-shaped  plateaus,  like  the  Bohemian  and 
Transylvanian,  are  thus  formed. 

The  Western  Division  includes  most  of  the  mountains 
of  France,  as  the  Cevennes,  the  mountains  of  Auvergne, 
and  the  Vosges  Mountains.  * 

The  Central  Division  includes  the  Jura  Mountains  in 
Switzerland,  the  Swiss  and  the  Bavarian  plateaus,  the 
Black  Forest  Mountains,  the  Hartz  Mountain;:.-,  and  the 
Bohemian  plateau. 

The  Eastern  Division  includes  most  of  the  mountains 
of  Austria,  as  the  Carpathians,  the  Hungarian  Forest,  and 
the  Transylvanian  Mountains. 

125.  The  three  projections  on  the  south  are  the 


three  mountainous  peninsulas  of  Southern  Eu- 
rope : 

The  Iberian  Peninsula,  including  Spain  and 
Portugal ; 

The  Italian  Peninsula ; 

The  Turco-Grecian  Peninsula. 

The  Iberian  Peninsula. — The  principal  mountains  are 
the  Sierra  Estrella,  the  mountains  of  Castile,  and  the 
Sierra  Nevada.  The  Pyrenees  separate  the  Peninsula  from 
France.  The  Cantabrian  Mountains  extend  along  the 
northern  coast. 

The  Italian  Peninsula  contains  the  Apennines,  ex- 
tending mainly  in  the  direction  of  the  north-western 
trend. 

The  Turco-Grecian  Peninsula.— The  Dinaric  Alps 
extend  along  the  coast  of  the  Adriatic ;  the  Balkan  Moun- 
tains extend  from  east  to  west,  through  Turkey ;  and  the 
Pindus  from  north  to  south,  through  Turkey  and  Greece. 

126.  The  Secondary  Mountain-Systems  of  Eu- 
rope comprise  the  system  of  the  Scandinavian 
peninsula,  the  Ural  Mountains,  and  the  Cauca- 
sus Mountains. 

The  System  of  the  Scandinavian  Peninsula 
includes  the  elevations  of  Norway  and  Sweden. 
With  the  exception  of  the  Kiolen  Mountains  in 
the  north,  the  system  does  not  embrace  distinct 
mountain-ridges,  but  consists  mainly  of  a  series 


Fig.  48.    Fiord  on  Norway  Coast. 

of  broad  plateaus  that  descend  abruptly  on  the 
west  in  numerous  deeply-cut  valleys  called  fiords, 
through  which  the  sea  penetrates  nearly  to  the 
heart  of  the  plateaus.  Fiords  are  valleys  that 
were  deeply  eroded  by  slowly  moving  masses  of 


50 


PHYSICAL    GEOGRAPHY. 


ice,  called  glaciers,  and  subsequently  partially  sub- 
merged. On  the  east  the  slopes  are  more  gradual, 
and  are  occupied  by  numerous  small  lakes. 

The  System  of  the  Urals  is  composed  of  a 
moderately  elevated  range  extending  from  the 
Arctic  Ocean  on  the  north  to  the  plains  of  the 
Caspian  on  the  south.  The  elevated  island  of 
Nova  Zembla  may  be  considered  as  forming  a 
part  of  its  northern  prolongation. 

The  Caucasus  Mountains  bear  peaks  exceeding 
in  elevation  those  of  the  Alps.  They  belong, 
however,  more  properly  to  the  elevations  of 
Asia. 

127.  The  Great  Low  Plain  of  Europe  lies  be- 
tween the  predominant  and  secondary  mountain- 


systems,  and  stretches  north-eastwardly  from  the 
Atlantic  to  the  Arctic.  It  is  remarkably  level, 
and  is  highest  in  the  middle,  where  the  Valdai 
Hills  form  the  principal  watershed  of  Europe. 
Westward  the  plain  is  continued  under  the  North 
Sea  to  the  British  Isles,  where  a  few  inconsider- 
able elevations  occur. 

South  of  the  Alps  the  large  plain  of  the  Po 
River  stretches  across  the  northern  part  of  Italy. 

128.  Approximate  Dimensions  of  Europe. 
Area  of  continent,  3,700,000  square  miles. 
Coast  line,  19,500  miles. 

Greatest  breadth  from  north  to  south,  2400  miles. 
Greatest  length  from    north-east  to  south-west,  3370 
miles. 

Culminating  point,  Mont  Blanc,  15,787  feet. 


Fig.  49^    Orographic  Chart  of  Asia^    (Light  portions,  mountains ;  shaded  portions,  plains.) 
1,  Himalaya  Mountains;  2,  Karakorum;  3,  Kuen-lun;  4,    Belor;  5,  Thian   Shan;  6,  Altai;   7,  Great  Kinghan;  8,  Yablonoi;  9,  Naullng; 
10,  Peling;  11,  Vindhya;  12,  Ghauts;  13,  Hindoo-Koosh ;  14,  Elburz;  15,  Suliman;  16,  Zagros;  17,  Taurus;  18,  Caucasus;  19,  Asiatic  Island  Chain. 


IV.     ASIA. 

129.  Surface  Structure.  —  The  Predominant 
Mountain-System  is  in  the  south. 

The  Secondary  Systems  surround  the  Predomi- 
nant System. 

The  Great  Low  Plain  is  on  the  north  and  west, 


and  lies  between  the  mountain-systems  of  Asia 
and  the  secondary  system  of  the  Urals. 

Europe  and  Asia  are  sometimes  considered  as  geographic- 
ally united  in  one  grand  division  called  Eurasia. 

130.  The  mountain-systems  of  Asia  are  nearly 
all  connected  in  one  huge  mass  which  extends  in 


RELIEF  FORMS  OF  THE  CONTINENTS. 


51 


the  line  of  the  north-east  trend,  from  the  Arctic  to 
the  Indian  Ocean.  Though  in  reality  one  vast 
system,  yet  they  are  most  conveniently  arranged 
in  one  predominant  and  several  secondary  systems. 
The  Predominant  System  is  the  plateau  of 
Thibet,  the  loftiest  table-land  in  the  world.  It 
is  between  15,000  and  16,000  feet  high,  and  is 
crossed  by  three  huge,  nearly  parallel,  mountain- 
ranges  :  the  Himalayas  on  the  south,  the  Kuen- 
lun  on  the  north,  and  the  Karahorum  between 
them.     The   Himalayas,   the   loftiest   mountains 


Fig.  50.    Himalaya  Mountains. 

in  the  world,  rise  abruptly  from  the  plains  of 
Northern  Hindostan.  Like  the  Alps,  their  axis 
is  curved,  but  in  the  opposite  direction.  The 
breadth  of  the  system  varies  from  100  to  200 
miles  ;  the  length  is  about  1500  miles.  The  high- 
est point  is  Mount  Everest,  29,000  feet  above  the 
sea ;  it  is  the  culminating  point  of  the  Asiatic  con- 
tinent and  of  the  world.  Kunchinjunga  and  Dha- 
walaghiri  are  scarcely  inferior  in  height. 

131.  The  Secondary  Systems  lie  on  all  sides  of 
the  predominant  system,  though  mainly  on  the 
north  and  east  of  the  predominant  system.  Like 
Europe,  the  Asiatic  continent  projects  on  the 
south  in  the  three  mountainous  peninsulas  of 
Arabia,  Hindostan,  and  Indo-China. 

On  the  north  and  east  of  the  plateau  of  Thibet 
is  an  extended  region  called  the  plateau  of  Gobi, 
considerably  lower  than  the  surrounding  country. 
The  Kuen-lun  and  Great  Kinghan  Mountains 
bound  it  on  the  south  and  east,  and  the  Altai 


Mountains  on  the  north.  On  the  west  lie  the 
Thian  Shan  and  Altai,  which  by  their  open  val- 
leys afford  ready  communication  with  the  low 
plains  on  the  west. 

The  plateau  of  Gobi  varies  in  average  height  from  2000 
to  4000  feet.  The  greatest  depression  is  in  the  west,  and 
is  occupied  by  Lake  Lop  and  the  Tarim  River.  A  small 
part  of  the  region  near  the  mountain-slopes  is  moderately 
fertile,  the  remainder  is  mainly  desert. 

The  Altai  Mountains  are  but  little  known,  but  some  of 
their  peaks  exceed  12,000  feet.  They  are  continued  east- 
ward by  the  Yablonoi  Mountains.  East  of  the  plateau  of 
Gobi  a  rauge  extends  north-easterly  through  Mantchooria. 

On  the  south  and  west  of  Thibet  lie  the  pla- 
teaus of  Iran,  Armenia,  and  Asia  Minor. 

The  Plateau  of  Iran  includes  Persia,  Afghan- 
istan, and  Beloochistan.  It  is  a  basin-shaped 
region  from  3000  to  5000  feet  high.  The  Elburz 
and  Hindoo-Koosh  Mountains  form  its  borders  on 
the  north,  the  Suliman  on  the  east,  and  the  Za- 
gros  on  the  south  and  west. 

The  Suliman  Mountains  rise  abruptly  from  the  plains 
of  the  Indus.  Across  these  mountains  occurs  the  only 
practicable  inland  route  between  Western  Asia  and  the 
Indies. 

The  Plateaus  of  Armenia  and  of  Asia  Minor 
lie  west  of  the  Plateau  of  Iran.  Armenia  is  8000 
feet  high,  and  bears  elevated  mountains :  Mount 
Ararat,  16,900  feet,  is  an  example.  On  the  west, 
the  peninsula  of  Asia  Minor,  or  Anatolia,  extends 
between  the  Black  and  Mediterranean  Seas,  and 
is  traversed  by  the  Taurus  Mountains. 

The  Caucasus  Mountains  lie  north  of  the  pla- 
teau of  Armenia.  They  are  an  elevated  range 
extending  between  the  Black  and  Caspian  Seas, 
and  form  part  of  the  boundary-line  between  Eu- 
rope and  Asia.  Mount  Elburz,  the  "  Watch- 
Tower,"  the  culminating  peak,  is  18,493  feet 
high. 

The  Arabian  Plateau  occupies  the  entire  penin- 
sula of  Arabia.  It  is  separated  from  the  plateau 
jf  Iran  by  the  Persian  Gulf  and  the  valleys  of 
the  Tigris  and  the  Euphrates. 

The  Plateau  of  Deccan  occupies  the  lower  part 
of  the  peninsula  of  Hindostan.  It  is  crossed  on 
the  north  by  the  Vindhya  Mountains,  and  along 
the  coasts  by  the  Eastern  and  Western  Ghauts. 

The  Peninsula  of  Indo-China  is  traversed  by 
a  number  of  mountain-ranges  which  diverge  from 
the  eastern  extremity  of  the  Himalayas.  The 
Nanling  and  Peling  extend  from  east  to  west 
through  China. 

132.  The  Great  Low  Plain  is,  in  reality,  but  a 
continuation  of  the  European  plain.  It  extends 
from  the  Arctic  Ocean  south-westerly  to  the  Cas- 


52 


PHYSICAL    GEOGRAPHY. 


pian  and  Black  Seas.  It  is  hilly  on  the  east,  but 
level  on  the  west.  South  of  the  60th  parallel  it 
is  comparatively  fertile.  Around  the  shores  of 
the  Arctic  are  the  gloomy  Tundras. 

The  Tundras  are  vast  regions  which  in  summer  are 
covered  with  occasional  moss-beds,  huge  shallow  lakes, 
and  almost  interminable  swamps,  and  in  winter  with  thick 
ice.  The  tundras  are  caused  as  follows :  The  rivers  that 
flow  over  the  immense  plain  of  Asia  rise  in  the  warmer 
regions  on  the  south.  Their  upper  courses  thawing  while 
the  lower  courses  are  still  ice-bound,  permits  large  quan- 
tities of  drift  ice  to  accumulate  at  their  mouths,  which, 
damming  up  the  water,  causes  it  to  overflow  the  adjoining 
country. 

Depressions  of  the  Caspian  and  Sea  of  Aral. — 
Two  remarkable  depressions  occur  in  the  basins 
of  the  Caspian  and  Sea  of  Aral,  and  that  of  the 
Dead  Sea.  These  are  all  considerably  below  the 
level  of  the  ocean.  The  waters  of  the  Caspian 
and  Sea  of  Aral  were  probably  once  connected 
in  a  great  inland  sea. 


The  Smaller  Asiatic  Plains  are  drained  by 
several  river-systems.  These  are  the  Plain  of 
Mantchooria,  drained  by  the  Amoor;  the  Plain 
of  China,  drained  by  the  Hoang-Ho  and  the 
Yang-tse-Kiang ;  the  Plain  of  India,  drained  by 
the  Indus,  the  Ganges,  the  Brahmapootra,  and 
the  Irrawaddy ;  and  the  Plain  of  Persia,  drained 
by  the  Tigris  and  the  Euphrates. 

133.  Approximate  Dimensions  of  Asia. 

Area  of  continent,  17,500,000  miles. 

Coast  line,  35,000  miles. 

Greatest  length  from  north-east  to  south-west,  7500  miles. 

Greatest  breadth  from  north  to  south,  5166  miles. 

Culminating  point,  Mount  Everest,  29,000  feet. 

134.  Comparison  of  the  Relief  Forms  of  Eu- 
rope and  Asia. — In  both  Europe  and  Asia  the 
chief  elevations  are  in  the  south  and  the  great  low 
plains  in  the  north.  Asia,  like  Europe,  extends 
toward  the  south  in  three  great  peninsulas :  Ara- 
bia, Hindostan,  and  Indo-China. 


Fig,  51.    Section  of  Asia  from  North  to  South. 
1,  Cape  Comorin;  2,  Deccan;  3,  Plain  of  India;  4,  Himalayas;  5,  Everest;  6,  Kuen-lun;    7,  Karakorum ;  8,  Thibet;  9,  Upper  Tartary;  10, 
Ararat ;  11,  Elburz ;  12,  Thian  Shan ;  13,  Altai ;  14,  Mountains  of  Kamtchatka ;  15,  Arctic  Ocean ,  mouth  of  Yenesei. 


Fig,  52,    Orographic  Chart  of  Africa. 
(Light  portions  represent  mountains ;  shaded  portions,  plains.) 
1,  Abyssinian  Plateau;  2,  3,  Kenia  and  Kilimandjaro ;  4,  Lupata; 
6,  Dragon;  6,  Nieu  veldt;  7,  Mocambe;  8,  Crystal;  9,  Cameroons;  10, 
Kong;  11,  Atlas;  12,  Lake  Tchad;  13,  Madagascar. 


V.     AFRICA. 

135.  Surface  Structure. — Nearly  the  entire  con- 
tinent of  Africa  is  a  moderately  elevated  plateau. 
It  therefore  has  no  great  low  plains ;  but  the  in- 
terior is  lower  than  the  marginal  mountain-sys- 
tems, and  in  this  respect  the  true  continental  type, 
high  borders  and  a  low  interior,  is  preserved. 

136.  The  Predominant  Mountain-System  is  in 
the  east. 

The  Secondary  Systems  are  in  the  south,  west, 
and  north. 

The  great  interior  depression  is  in  the  middle, 
and  is  surrounded  by  the  predominant  and  sec- 
ondary systems.  * 

A  narrow,  low  plain  extends  along  most  of  the 
coast.  It  is  broadest  on  the  north-west,  between 
the  plateau  of  the  Sahara  and  the  Atlas  Moun< 
tain-system. 

137.  The  Predominant  Mountain-System  ex- 
tends along  the  entire  eastern  shore,  from  the 
Mediterranean  Sea  to  the  southern  extremity  of 
the  continent.     It  is  highest  near  the  centre,  in 


RELIEF  FORMS  OF  THE  CONTINENTS. 


53 


the  plateaus  of  Abyssinia  and  Kaffa.  The  culmi- 
nating point  is  probably  to  be  found  in  the  vol- 
canic peaks  of  Kenia  and  Kilimandjaro,  whose 
estimated  heights  are  taken  at  about  19,000  feet. 
In  the  Abyssinian  plateau,  on  the  north,  an  aver- 
age elevation  of  from  6000  to  8000  feet  occurs. 
Upon  this,  rising  in  detached  groups,  are  peaks 
the  highest  of  which  are  over  15,000  feet. 

From  the  Abyssinian  plateau  the  system  is  con- 
tinued northward  to  the  Mediterranean  by  a  suc- 
cession of  mountains  which  stretch  along  the 
western  shores  of  the  Red  Sea.  Some  of  the 
peaks  are  from  6000  to  9000  feet.  South  of  the 
plateau  of  Kaffa  the  system  is  continued  by  the 
Zmpata  and  Dragon  Mountains  to  the  southern 
extremity  of  the  continent.  The  Zambesi  and 
Limpopo  Rivers  discharge  their  waters  into  the 
Indian  Ocean  through  deep  breaks  in  the  system. 

138.  Secondary  Systems. — On  the  south  the 
Nieuveldt  and  Snow  Mountains  stretch  from  east 
to  west,  with  peaks  of  over  10,000  feet.  Table 
Mountain  is  on  the  south. 


Fig.  53.    Table  Mountain. 

On  the  west  the  Mocambe  and  Crystal  Mountains 
extend  from  the  extreme  south  to  the  Gulf  of 
Guinea.  Near  the  northern  end  of  this  range, 
but  separate  from  it,  are  the  volcanic  peaks  of 
the  Cameroons  Mountains,  13,000  feet  high. 

The  Kong  Mountains  extend  along  the  north- 
ern shores  of  the  Gulf  of  Guinea  in  a  general 
east-and-west  direction.  Some  of  the  peaks  are 
snow-capped.  In  the  extreme  north  of  Africa 
are  the  Atlas  MoHtntains,  'which  rise  from  the 
summit  of  a  moderately  elevated  plateau.  Some 
of  the  peaks  are  13,000  feet  high. 

139.  The  Great  Interior  Depression  north  of 
the  equator  is  divided  into  two  distinct  regions. 
A  straight  line  extending  from  Cape  Guardafui 
to  the  northern  shores  of  the  Gulf  of  Guinea 
marks    the    boundary.      The    mountain-systems 


north  of  this  line  have  a  general  east-and-west 
direction  ;  those  south  of  it  have  a  general  north- 
and-south  direction. 

The  Plateau  of  the  Sahara  occupies  the  north- 
ern part  of  the  interior  depression.  Its  general 
elevation  is  about  1500  feet,  though  here  and 
there  plateaus  of  from  4000  to  5000  feet  occur, 
and  even  short  mountain-ranges  with  peaks  of 
6000  feet.  The  main  portion  of  the  region  is  cov- 
ered with  vast  sand-fields,  with  occasional  rocky 
masses,  and  is  one  of  the  most  absolute  deserts 
in  the  world. 


■*ju&-^^*- 


Fig.  54,    Desert  of  Sahara. 

Near  long.  14°  E.  from  Greenwich,  in  the  district  of 
Fezzan,  the  plateau  is  divided  from  north  to  south  by  a 
broad  valley.  In  this  occur  many  remarkable  depressions, 
some  of  which  are  several  hundred  feet  below  the  level  of 
the  Mediterranean.  Here  fertile  spots,  called  oases,  are 
common. 

South  of  the  Sahara  is  the  Soudan,  a  remark- 
ably well-watered  and  fertile  region.  Lake  Tchad 
occupies  the  greatest  depression.  The  interior, 
which  lies  south  of  this,  is  but  little  known.  It 
is  probably  a  moderately  elevated  plateau.  Ex- 
tensive lake-basins — Albert  and  Victoria  Nyan- 
zas  and  Tanganyika — lie  near  the  predominant 
mountain-system. 

140.  Approximate  Dimensions  of  Africa. 
Area  of  continent,  12,000,000  square  miles. 
Coast  line,  16,000  miles. 

Greatest  breadth  from  east  to  west,  4800  miles. 
Greatest  length  from  north  to  south,  5000  miles. 
Culminating    point,    Mount    Kenia,   or    Kilimandjaro, 
about  19,000  feet. 


54 


PHYSICAL    GEOGRAPHY. 


Fig.  55.    Orographic  Chart  of  Australia. 
(White  portions,  mountains ;  shaded  portions,  plains.) 
1,  Australian  Alps;  2,  Kosciusko;   3,  4,  5,  Secondary  Systems;  6, 
Murray  Eiver. 

VI.    AUSTRALIA. 

141.  Surface  Structure.  —  The  Predominant 
Mountain-System  is  in  the  east. 

The  Secondary  Systems  are  in  the  west  and 
north-west. 

The  Great  Low  Plain  lies  between  the  pre- 
dominant and  secondary  systems,  and  slopes 
gently  to  the  southern  coast. 

The  Predominant  System  extends  along  the 
entire  eastern  shore,  from  Torres  Straits  to  the 
southern  extremity  of  Tasmania.  It  is  for  the 
most  part  composed  of  broad  plateaus.  The 
system  is  highest  in  the  south-east,  where  the 
name  Australian  Alps  is  given  to  the  range. 
Mount  Kosciusko,  7000  feet,  probably  forms  the 
culminating  point  of  the  Australian  continent. 

The  system  descends  abruptly  on  the  east,  but 
on  the  west  it  descends  by  gentle  slopes  to  the 
low  plains  of  the  interior. 

142.  The  Secondary  Systems,  on  the  west  and 
north-west,  are  of  but  moderate  elevation. 

143.  The  Great  Low  Plain  lies  in  the  interior.  Ac- 
curate information  as  to  its  peculiarities  is  yet  wanting. 
A  moderate  elevation  on  the  north  connects  the  eastern 
and  western  systems.  The  south-eastern  portion,  which 
is  the  hest  known,  is  well  watered  and  remarkably  fertile. 
Basin-shaped  valleys  are  found  in  the  west.  The  lower 
parts  are  occupied  by  Lake  Eyre,  Torrens,  and  Gairdner. 


144.  Approximate  Dimensions  of  Australia. 
Area  of  continent,  3,000,000  square  miles. 
Coast  line,  10,000  miles. 

Greatest  length  from  east  to  west,  2400  miles. 
Greatest  breadth  from  north  to  south,  2000  miles. 
Culminating  point,  Mount  Kosciusko,  7000  feet. 

145.  Contrasts  of  Africa  and  Australia. — In 

the  north,  the  African  continent  resembles  Europe 
and  Asia  in  the  arrangement  of  its  forms  of 
relief.  In  the  south,  it  resembles  the  Americas. 
As  a  whole,  the  African  continent  resembles 
Australia  more  closely  than  any  other.     In  both 


Fig.  56.    Australian  Scenery. 

Africa  and  Australia  the  predominant  system  is 
in  the  east,  and  extends  along  the  entire  coast. 
In  each  the  secondary  systems  are  in  the  west 
and  north.  But  Africa  terminates  in  a  plateau 
which  descends  abruptly  to  the  sea,  while  Australia 
is  terminated  by  a  great  low  plain  which  descends 
by  long,  gentle  slopes  from  the  interior. 


SYLLABUS. 


<*<*c 


Eock-masses  are  divided,  according  to  their  origin,  into 
igneous,  aqueous,  and  metamorphic.  According  to  their  con- 
dition, into  stratified  and  unstratified.  According  to  the 
presence  or  absence  of  organic  remains,  into  fossiliferous 
and  non-fossiliferous.    Stratified  rocks  are  sometimes  called 


fragmental.    Unstratified  rocks  are  sometimes  called  crys- 
talline.   Aqueous  rocks  are  sometimes  called  sedimentary. 

Aqueous  rocks  are  stratified.  Igneous  rocks  are  un- 
stratified. Metamorphic  rocks  were  originally  stratified, 
but  lost  their  stratification  through  metamorphism. 


REVIEW    QUESTIONS. 


55 


Aqueous  rocks  may  contain  fossils.  Igneous  rocks  never 
contain  fossils.  Metamorphic  rocks,  in  rare  instances,  may 
contain  fragments  of  fossils. 

Geological  time  is  divided  into  Archaean,  Palseosoic,  Meso- 
zoic,  and  Cenozoic. 

Archaean  Time  includes  the  Azoic  and  the  Eozoic  Ages. 

Palaeozoic  Time,  or,  as  it  is  sometimes  called,  the  Pri- 
mary, includes  the  Silurian,  Devonian,  and  Carboniferous 
Ages. 

Mesozoic  Time,  or  the  Secondary,  includes  the  Age  of 
Eeptiles. 

Cenozoic  Time  includes  the  Age  of  Mammals,  or  the  Ter- 
tiary, and  the  Era  of  Man,  or  the  Quaternary  Age. 

The  changes  to  which  the  earth's  crust  is  now  subject 
are  produced  by  the  following  agencies: 

1.  By  the  winds ;  2.  By  the  moisture  of  the  atmosphere; 
3.  By  the  action  of  running  water ;  4.  By  the  action  of 
ocean  waves ;  5.  By  the  agency  of  man ;  6.  By  the  con- 
traction of  a  cooling  crust. 

There  is  more  water  than  land  surface  on  the  earth,  in 
proportion  of  25  :  9,  or  as  5a :  3a. 

The  land-masses  surround  the  north  pole  in  the  shape 
of  an  irregular  ring. 

Nearly  all  the  land-areas  are  collected  in  one  hemi- 
sphere, and  the  water-areas  in  another. 

The  Land  Hemisphere  comprises  the  whole  of  North 
America,  Europe,  and  Africa,  all  of  Asia  except  a  small 
part  of -the  Malay  Peninsula,  and  the  greater  part  of  South 
America. 

The  Water  Hemisphere  comprises  the  whole  of  Australia 
and  the  southern  portions  of  South  America  and  the  Ma- 
lay Peninsula. 

The  northern  continents  are  almost  entirely  in  the  tem- 
perate latitudes ;  the  southern  are  mainly  in  the  tropics. 

The  land-masses  may  be  divided  into  three  doublets, 
consisting  of  pairs  of  northern  and  southern  continents, 
almost  or  entirely  separated  from  each  other. 

There  are  two  great  systems  of  trends  or  lines  of  direc- 
tion, along  which  the  continents,  the  coast  lines,  the 
mountain-ranges,  the  oceanic  basins,  and  the  island  chains 
are  arranged.   These  trends  are  north-east  and  north-west. 

The  northern  continents  are  characterized  by  deeply  in- 
dented coast  lines ;  the  southern  are  comparatively  simple 
and  unbroken.  Europe  is  the  most,  and  Africa  the  least, 
deeply  indented  of  the  continents. 

In  proportion  to  her  area,  Europe  has  three  times  as 
much  coast  line  as  Asia,  and  four  times  as  much  as  Africa. 

One-seventeenth  of  the  land-area  is  composed  of  islands. 

Islands  are  either  continental  or  oceanic. 

There  are  four  successive  stages  in  the  formation  of  a 
coral  island  or  atoll :  1.  The  fringing  reef ;  2.  The  barrier 
reef;  3.  The  encircling  reef;  4.  The  coral  island  or  atoll. 

The  greatest  elevations  and  depressions  in  the  earth's 
surface  are  small  when  compared  with  its  size. 


Low  lands  are  either  plains  or  hills. 

High  lands  are  either  plateaus  or  mountains. 

Plains  are — 1.  Undulating;  2.  Marine;  3.  Alluvial. 

Mountains  were  produced  by  the  contraction  of  the 
crust,  producing  a  lateral  pressure  on  thick,  extended  de- 
posits of  sedimentary  rocks.  Slaty  cleavage  was  caused 
by  this  lateral  pressure. 

Valleys  are  either  longitudinal  or  transverse. 

All  continents  have  high  borders  and  a  low  interior. 
The  highest  border  faces  the  deepest  ocean. 

The  greatest  prolongation  of  a  continent  is  that  of  its 
predominant  mountain-system.  The  culminating  point  is 
always  out  of  the  centre. 

North  and  South  America  resemble  each  other  in  the 
arrangement  of  their  relief  forms.  Their  predominant 
systems  are  in  the  west ;  their  secondary  systems  are  in 
the  east;  their  great  low  plains  are  between  the  predomi- 
nant and  secondary  systems. 

The  predominant  system  of  North  America  is  the  Pa- 
cific mountain-system.  The  secondary  systems  are — the 
Appalachian  system,  the  plateau  of  Labrador,  the  Height 
of  Land,  and  the  Arctic  plateau. 

The  predominant  system  of  South  America  is  the  sys- 
tem of  the  Andes.  The  secondary  systems  are — the  pla- 
teaus of  Guiana  and  Brazil.  The  great  low  plains  are — 
the  Llanos  of  the  Orinoco,  the  Selvas  of  the  Amazon,  and 
the  Pampas  of  the  La  Plata. 

Europe  and  Asia  resemble  each  other.  Their  predomi- 
nant systems  are  in  the  south ;  their  great  low  plains  are 
north  of  their  predominant  systems.  The  predominant 
system  of  Europe  is  in  the  south. 

The  secondary  systems  are — the  mountains  of  the  Scan- 
dinavian Peninsula,  the  Ural  Mountains,  and  the  Caucasus 
Mountains. 

The  predominant  mountain-system  of  Asia  is  the  pla- 
teau of  Thibet. 

The  secondary  systems  are — the  plateau  of  Gobi,  the 
Thian-Shan  and  Altai  Mountains,  the  plateau  of  Indo- 
China,  the  plateau  of  Deccan,  the  plateau  of  Iran,  the  pla- 
teau of  Asia  Minor,  and  the  plateau  of  Arabia. 

Africa  and  Australia  resemble  each  other.  Their  pre- 
dominant systems  are  in  the  east;  their  secondary  systems 
are  in  the  west  and  north ;  their  depressed  areas  are  be- 
tween the  two. 

The  predominant  mountain-system  of  Africa  includes 
the  mountains  of  the  eastern  coast. 

The  secondary  systems  include  the  Nieuveldt  and  Snow 
Mountains  in  the  south,  the  Mocambe,  Crystal,  Cameroons, 
and  Kong  Mountains  in  the  west,  and  the  Atlas  Mountains 
in  the  north. 

The  predominant  mountain-system  of  Australia  includes 
the  mountains  of  the  eastern  coast. 

The  secondary  systems  include  those  found  in  the  south w 
west,  and  north. 


REVIEW  QUESTIONS. 

o<>x*;oo 


What  two  elementary  substances  form  the  greater  part 
by  weight  of  the  earth's  crust  ? 

Into  what  classes  may  rocks  be  divided  according  to 
their  condition  ?  According  to  their  origin  ?  According 
to  the  presence  or  absence  of  fossils? 

What  is  palaeontology  ? 


Define  Archaean  Time,  Palaeozoic  Time,  Mesozoic  Time, 
and  Cenozoic  Time. 

Explain  the  nature  of  the  changes  which  the  atmo- 
sphere is  now  effecting  in  the  earth's  surface.  Which  the 
water  is  effecting.     Which  man  is  effecting. 

What  must  be  the  areas  of  two  squares  whose  areas 


56 


PHYSICAL    GEOGRAPHY. 


represent  the  relative  land-  and  water-areas  of  the  earth  ? 
What  are  the  actual  areas  in  square  miles? 

How  would  you  draw  a  circle  around  the  earth  which 
will  divide  it  into  land  and  water  hemispheres? 

Do  the  continents  extend  farther  to  the  north  pole  or  to 
the  south  pole  ? 

What  do  you  understand  by  lines  of  trend  ? 

Which  have  the  more  diversified  coast  lines,  the  north- 
ern or  the  southern  continents? 

Define  continental  and  oceanic  islands,  and  give  exam- 
ples of  each.  Why  are  continental  islands  to  be  regarded 
as  detached  portions  of  the  neighboring  mainland? 

Name  the  American  island  chains.     The  Asiatic  chains. 

Describe  the  Australasian  island  chain.  The  Polynesian 
chain. 

Which  are  the  higher,  volcanic  islands  or  coral  islands  ? 
Why? 

Name  the  four  principal  steps  or  stages  in  the  progress 
of  formation  of  a  coral  island. 

Is  the  coral  island  built  by  the  coral  animalcule  or  by 
the  waves?    Explain  your  answer. 

What  is  Darwin's  theory  for  the  presence  of  a  lagoon 
within  the  reef? 

What  is  the  difference  between  a  plain  and  a  plateau? 
A  mountain  and  a  hill? 

Define  mountain-system.     A  chain.     A  knot. 

What  is  the  name  of  the  highest  plateau  in  the  world  ? 
Of  the  largest  plain  ? 

In  what  different  ways  were  plains  formed  ? 

Distinguish  between  a  longitudinal  and  a  transverse 
valley.  Explain  the  manner  in  which  mountains  were 
formed. 

Give  a  short  account  of  the  surface  structure,  or  the 
arrangement  of  the  high  and  low  lands,  of  North  America. 
Of  South  America.  Of  Europe.  Of  Asia.  Of  Africa,  and 
of  Australia.  Which  of  these  resemble  each  other?  In 
what  respect  do  they  all  resemble  one  another? 

Name  the  culminating  points  of  each  of  the  continents. 

Name  the  predominant  and  secondary  mountain-systems 
of  each  of  the  continents. 

How  many  times  larger  is  Asia  than  Australia?  Than 
Europe  ?    Africa  ?    North  America  ?    South  America  ? 

North  America. 
Name  the  principal  mountains  of  the  Pacific  mountain- 
system.    Which  contains  the  culminating  point  of  the 
continent  ? 


Where  is  the  Great  Basin  ?  By  what  mountains  is  it 
surrounded  ? 

Name  the  principal  mountains  of  the  Appalachian  sys- 
tem. 

Is  the  greater  portion  of  the  area  of  North  America 
above  or  below  1000  feet? 

What  rivers  drain  the  great  low  plain  of  North  Amer- 
ica? 

South  America. 

Name  the  principal  plateaus  of  the  Andes.  Through 
which  does  the  equator  pass?  Which  contains  Lake  Titi- 
caca? 

Where  is  the  plateau  of  Guiana  ?    Of  Brazil  ? 

What  three  large  river-systems  drain  the  great  low  plain 
of  South  America  ?  What  resemblances  can  you  find  be- 
tween the  directions  of  these  rivers  and  those  which  drain 
North  America  ? 

Europe. 

Describe  the  chain  of  the  Alps. 

What  river-systems  divide  its  northern  slope  into  three 
divisions  ?   Name  the  principal  mountains  of  each  division. 

What  three  peninsulas  project  southward  from  the  south- 
ern slopes  of  the  predominant  mountain-system? 

Name  the  principal  mountains  of  each  peninsula. 

Name  the  great  low  plains  of  Europe. 

Asia. 

What  mountains  form  the  northern  boundary  of  the 
plateau  of  Thibet?  The  southern  boundary?  The  north- 
ern boundary  of  the  plateau  of  Mongolia?  The  eastern 
boundary?    What  mountains  extend  through  China? 

What  mountains  form  the  boundaries  of  the  plateau  of 
Iran  ?    Is  Arabia  a  plateau  or  a  plain  ? 

Is  the  land  north  of  the  Sea  of  Aral  high  or  low? 

In  which  line  of  trend  do  the  mountainous  elevations 

of  Asia  extend  ? 

Africa. 

What  portions  of  Africa  are  high  ?  What  portions  are 
low? 

Where  is  the  predominant  system?  Where  is  the  cul- 
minating point?    What  part  of  the  interior  is  low? 

Where  are  the  Mocambe  Mountains  ?  The  Crystal  Moun- 
tains, the  Cameroons,  the  Atlas,  the  Kong,  the  Lupata,  and 

the  Dragon? 

Australia. 

Where  is  the  predominant  mountain-system?    The  sec- 
ondary system  ? 
Where  is  Mount  Kosciusko?    The  Murray  River? 


Part  III. 


THE   WATER, 


►oXKc 


By  contact  of  air  with  the  water-areas,  an  immense  quantity  of  invisible  vapor  passes  into  the 
atmosphere,  from  which,  when  sufficiently  cooled,  it  re-appears  and  descends  as  fog,  dew,  rain,  hail,  sleet, 
or  snow.  It  then,  in  greater  part,  drains  through  various  lake-  and  river-systems  into  the  ocean,  where 
it  is  either  again  evaporated,  or  carried  about  in  waves,  tides,  or  currents.  This  circulation  of  water 
never  ceases,  and  upon  it  depends  the  existence  of  all  life  on  the  earth. 


Section  I. 


CONTINENTAL.  WATERS. 


-ooX^c 


CHAPTER   I. 

Physical  Properties  of  Water. 

146.  Composition. — Water  is  formed  by  the 
combination  of  oxygen  and  hydrogen,  in  the  pro- 
portion, by  weight,  of  eight  parts  of  oxygen  to 
one  part  of  hydrogen  ;  or,  by  volume,  of  one  part 
of  oxygen  to  two  parts  of  hydrogen. 

147.  Properties.  —  Pure  water  is  a  colorless, 
transparent,  tasteless,  and  inodorous  liquid.     It 


freezes  at  32°  Fahr.,  and,  under  the  ordinary 
pressure  of  the  atmosphere,  boils  at  212°  Fahr. 

Water  exists  in  three  states :  solid,  liquid,  and  gaseous. 
Under  ordinary  circumstances  it  freezes  at  32°.  It  evapo- 
rates, or  passes  off  from  the  surface  as  vapor,  at  all  tempera- 
tures, even  at  32° ;  but  it  is  only  at  the  boiling-point  that 
the  vapor  escapes  from  the  mass  of  the  liquid  as  well  as 
from  the  surface. 

Heated  in  open  vessels,  under  the  ordinary  pressure  of 
the  atmosphere,  its  temperature  cannot  be  raised  higher  than 
212°,  any  increase  of  heat  only  causing  it  to  boil  more  rap- 
idly.    Heated  in  closed  vessels,  which  prevent  the  escape 

57 


58 


PHYSICAL    GEOGRAPHY. 


of  steam,  its  temperature  can  be  raised  very  high.  In 
such  cases  great  pressure  is  exerted  on  the  walls  of  the 
vessel.  Conversely,  on  high  mountains,  where  the  pres- 
sure of  the  atmosphere  is  lower  than  at  the  level  of  the 
sea,  water  boils  at  temperatures  lower  than  212°  Fahr. 

148.  Maximum  Density  of  Water. — A  pint  of 
cold  water  is  heavier  than  a  pint  of  warm  water, 
because  as  water  is  cooled  it  contracts  and  grows 
denser.  The  coldest  pint  of  water,  however,  is 
not  the  heaviest.  The  heaviest  pint  of  water  is 
water  at  the  temperature  of  39.2°  Fahr.  This 
temperature  is  therefore  called  the  temperature 
of  the  maximum  density  of  water.  If  water  at 
this  temperature  be  heated,  it  becomes  lighter,  or 
expands ;  if  water  at  this  temperature  be  cooled, 
it  also  becomes  lighter  or  expands  until  ice  is 
formed,  which  floats  on  the  water.  When  at  the 
temperature  of  its  maximum  density,  water  is 
7.2°  warmer  than  the  freezing-point. 

149.  Effect  of  the  Maximum  Density  of  Water 
on  its  Freezing. — If  water  continued  to  contract 
indefinitely  while  cooling  until  freezing  began, 
the  ice  first  formed  would  sink  to  the  bottom,  and, 
this  process  continuing,  the  entire  mass  would  soon 
become  solid.  In  this  manner  all  bodies  of  fresh 
water,  in  times  of  great  cold,  might  freeze  through- 
out ;  when,  not  even  the  heat  of  a  tropical  sun 
could  entirely  melt  them. 

But  for  this  curious  exception  in  the  physical  properties 
of  water,  at  least  three-fourths  of  the  globe  would  be  in- 
capable of  sustaining  its  present  life. 

The  entire  floor  of  the  ocean,  both  in  the  tropics  and  in 
the  temperate  and  the  polar  regions,  is  covered  with  a  layer 
of  cold,  salt  water  at  nearly  the  temperature  of  its  maxi- 
mum density.  In  the  tropics  the  surface-water  is  warmer 
and  lighter  than  this  dense  layer,  and  in  the  polar  re- 
gions it  is  colder  and  lighter. 

150.  Specific  Heat  of  Water.  —  Another  re- 
markable property  of  water — its  specific  heat — 
enables  it  to  play  an  important  part  in  the 
economy  of  the  world. 

The  specific  heat  of  a  body  is  the  quantity  of 
heat-energy  required  to  produce  a  definite  in- 
crease of  temperature  in  a  given  weight  of  that 
body. 

Water  has  a  very  great  specific  heat ;  that  is, 
a  given  quantity  of  water  requires  more  heat-energy 
to  warm  it,  and  gives  out  more  heat-energy  on  cool- 
ing, than  an  equal  quantity  of  any  other  common 
substance. 

The  quantity  of  heat  required  to  raise  a  pound  of  ice- 
cold  water  to  212°,  would  heat  a  pound  of  ice-cold  iron  to  a 
bright  red  heat,  or  to  about  1600°  Fahr. ;  or,  conversely,  a 
pound  of  boiling  water  cooling  to  the  freezing-point,  would 
give  out  as  much  heat  as  a  pound  of  red-hot  iron  cooling 
to  32°  Fahr. 


The  enormous  capacity  of  water  for  heat  is  of 
great  value  to  the  life  of  the  earth.  The  oceanic 
waters  are  vast  reservoirs  of  heat,  storing  heat  in 
summer  and  giving  it  out  in  winter.  The  great 
specific  heat  of  water  prevents  it  from  either  heat- 
ing or  cooling  rapidly.  Large  bodies  of  water, 
therefore,  prevent  great  extremes  of  heat  and 
cold. 

151.  Heat  Absorbed  or  Emitted  during  Change 
of  State. — During  the  conversion  of  a  solid  into 
a  liquid,  or  a  liquid  into  a  vapor,  a  large  quantity 
of  heat-energy  is  absorbed.  This  heat-energy  does 
not  increase  the  temperature  of  the  body,  and 
therefore  cannot  be  detected  by  the  thermometer. 
The  heat-energy  is  then  in  the  condition  of  stored 
or  potential  energy,  sometimes  called  latent  heat. 
When  the  vapor  condenses  into  a  liquid,  or  the 
liquid  freezes,  the  stored  heat-energy  again  becomes 
sensible  as  heat. 

In  freezing,  water  gives  out  heat  and  raises  the 
mean  temperature  of  the  atmosphere. 

In  melting,  ice  takes  in  heat  and  lowers  the  mean 
temperature  of  the  atmosphere. 

Water  has  a  higher  latent  heat  than  any  other 
common  substance. 

Stored  Seat-Energy  of  Ice- Cold  Water. — In 
order  to  heat  a  pound  of  water  1°  Fahr.  an 
amount  of  heat  called  a  heat-unit,  or  a  pound 
degree  is  required.  Before  one  pound  of  ice  at 
32°  Fahr.  can  melt  and  form  one  pound  of  water 
at  32°  Fahr.,  it  must  take  in  1J$  heat  units;  and 
yet  a  thermometer  plunged  in  the  water  from 
melting  ice  will  indicate  the  same  temperature  as 
when  entirely  surrounded  by  lumps  of  the  un- 
melted  material. 

The  great  latent  heat  of  ice-cold  water  has  an  important 
influence  on  the  freezing  of  large  bodies  of  water,  since, 
after  the  surface-layers  have  reached  the  temperature  of 
the  freezing-point,  they  have  still  142  heat-units  to  lose  be- 
fore they  can  solidify.  Again,  when  ice  reaches  a  tempera- 
ture of  32°  Fahr.,  it  has  still  142  heat-units  to  absorb  before 
it  can  melt.  Were  it  not  for  this  fact  destructive  floods 
would  often  result  from  the  rapid  melting  of  the  winter's 
accumulation  of  snow  and  ice. 

Stored  Heat-Energy  of  Water-  Vapor. — Before 
one  pound  of  water  can  pass  off  as  vapor,  it 
must  take  in  sufficient  heat  to  raise  nearly  1000 
pounds  of  water  1°  Fahr.  The  vapor  which  then 
escapes  is  still  at  the  same  temperature  as  the 
water  from  which  it  came.  The  1000  heat-units, 
or  pound-degrees  of  heat,  have  been  rendered  latent, 
and  have  no  influence  on  the  thermometer. 

When  the  vapor  in  the  air  is  condensed  as  rain, 
snow,  hail,  fog,  or  cloud  the  stored  heat-energy 


DRAINAGE. 


59 


again  becomes  sensible.  Much  of  the  vapor 
which  is  formed  in  the  equatorial  regions  is  car- 
ried by  the  winds  to  high  northern  latitudes, 
where,  on  condensing,  it  gives  out  its  heat  and 
moderates  the  intense  cold  which  would  otherwise 
exist. 

152.  Solvent  Powers. — Water  is  one  of  the  best 
solvents  of  all  common  substances.  During  the 
constant  washings  to  which  the  continents  are 
subjected  by  the  rains,  their  surfaces  are  cleansed 
from  decaying  animal  and  vegetable  matters, 
which  are  partly  dissolved  and  carried  by  the 
rivers  into  the  ocean.  The  atmospheric  waters 
in  the  same  way  cleanse  the  air  of  many  of  its 
impurities. 

153.  Water  is  the  Main  Food  of  Animals  and 
Plants. — By  far  the  greater  part  of  the  bodies  of 
animals  and  plants  is  composed  of  water.  With- 
out large  quantities  of  water  no  vigorous  life  can 
be  sustained  in  any  locality. 

Deserts  are  caused  entirely  by  the  absence  of 
water. 


CHAPTER   II. 
Drainage. 

154.  Drainage.  —  The  atmospheric  waters,  or 
those  which  fall  from  the  atmosphere  as  rain, 
hail,  or  snow,  either  sink  through  the  porous 
strata  and  are  drained  under  ground,  or  run 
directly  off  the  surface.  Thus  result  two  kinds 
of  drainage — Subterranean  and  Surface. 

155.  Subterranean  Drainage. — The  water  which 
sinks  through  the  porous  strata  continues  descend- 
ing until  it  meets  impervious  layers,  when  it  either 
runs  along  their  surface,  bursting  out  as  springs 
at  some  lower  level,  where  the  layers  outcrop,  or 
it  collects  in  subterranean  reservoirs.  The  origin 
of  all  springs  is  to  be  traced  to  subterranean 
drainage. 

Underground  streams  sometimes  attain  considerable  size. 
In  portions  of  the  Swiss  Jura  streams  burst  from  the  sides 
of  hills  in  sufficient  volume  to  turn  the  wheels  of  moder- 
ately large  mills.  In  a  few  instances  the  subterranean 
stream  can  be  navigated  for  considerable  distances,  as  in 
the  Mammoth  Cave  of  Kentucky,  or  in  the  Grotto  of 
Adelsberg,  near  Trieste. 

156.  Surface  Drainage. — The  water  which  is 
drained  directly  from  the  surface,  either  runs 
down  the  slopes  in  rivulets  and  rills,  which, 
uniting  with  larger  streams,  are  poured  directly 
into  the  ocean,  or  it  collects  in  the  depressions  of 


basin-shaped  valleys,  where,  having  no  connection 
with  the  ocean,  it  can  be  discharged  by  evapora- 
tion only.  Thus  arise  two  kinds  of  surface  drain- 
age— oceanic  and  inland. 

157.  Springs  are  the  outpourings  of  subterra- 
nean waters.  The  waters,  having  soaked  through 
the  porous  strata,  again  emerge  at  the  surface, 
either — 

(1.)  By  running  along  an  inclined,  impervious 
layer  of  clay,  hard  rock,  or  other  material  until 


Fig,  57.    Origin  of  Springs. 

they  emerge  at  some  lower  level,  where  the  strata 
outcrop;  or, 

(2.)  By  being  forced  upward  out  of  the  reser- 
voirs into  which  they  have  collected  by  the  pres- 
sure of  compressed  gas,  highly  heated  steam,  or, 
more  commonly,  by  the  pressure  of  a  communi- 
cating column  of  water. 

It  is  in  the  first  way  that  most  of  the  springs  of  moun- 
tainous districts  discharge  their  waters.  The  tilted  and 
broken  condition  of  the  strata  is  such  as  to  favor  the  es- 
cape along  some  of  the  many  layers  that  crop  out  on  the 
mountain-slopes.  The  springs  of  plains,  which  are  at  some 
distance  from  mountains,  discharge  their  waters  mainly  by 
the  methods  mentioned  under  the  second  heading. 

When  a  well  is  dug  in  most  porous  soils,  the  water  from 
the  porous  strata  on  the  sides  runs  in  and  partially  fills 
the  opening. 

158.  Classification  of  Springs.— Springs  are 
most  conveniently  arranged  in  different  classes 
according  to  peculiarities  in  the  size,  shape,  and 
depth  of  their  reservoirs,  and  the  nature  of  the 
mineral  substances  composing  the  strata  over  which 
the  waters  flow,  or  in  which  they  collect. 

The  Reservoirs  of  springs  are  the  places  where 


60 


PHYSICAL    GEOGRAPHY. 


the  waters  that  sink  into  the  ground  collect. 
Reservoirs  are  sometimes  large  subterranean 
basins,  but  more  frequently  are  merely  porous 
strata,  such  as  beds  of  sand  or  gravel,  which  lie 
between  impervious  layers  of  clay  or  hard  rock. 
The  water  collects  in  the  spaces  between  the  par- 
ticles of  sand  or  gravel. 

159.  Size  of  Reservoir. — When  the  reservoir 
is  large,  the  spring  is  constant;  when  small,  the 
spring  is  temporary. 

Constant  Springs  are  those  which  flow  continu- 
ally, and  are  but  little  affected  in  the  volume  of 
their  discharge  even  by  long-continued  droughts. 

Temporary  Springs  are  those  which  flow  only 
for  a  short  time  after  wet  weather,  drying  up  on 
the  appearance  of  even  moderate  droughts. 

The  quantity  of  water  discharged  by  a  spring  depends  on  the 
size  of  the  orifice  or  outlet  tube,  and  the  depth  of  the  outlet  be- 
low the  surface  of  the  water  in  the  reservoir.  The  flow  is 
proportional  to  the  square  root  of  the  depth.  That  is  to 
say,  if  with  a  given  depth  of  orifice  the  velocity  be  one 
foot  per  second,  in  order  to  make  the  water  escape  with 
twice  the  velocity  the  depth  must  be  increased  fourfold. 
The  actual  velocity  is  somewhat  less  than  this,  being  di- 
minished by  friction. 

Since  the  volume  discharged  by  some  springs 
is  very  considerable,  we  must  infer  that  their 
reservoirs  are  of  great  size.  Many  springs  prob- 
ably receive  the  drainage  from  hundreds  of 
square  miles  of  surface. 

160.  Shape  of  the  Reservoir. — When  the  out- 
let tube  of  the  reservoir  is  siphon-shaped,  the  dis- 
charge of  the  spring  becomes  periodical.     The 


Fig.  58.    A  Periodical  Spring. 

spring  continues  to  discharge  its  waters  for  a 
time,  and  then  stops  flowing,  even  during  wet 
weather.     After  a  certain  interval  it  again  dis- 


charges. The  times  during  which  the  spring  con- 
tinues to  discharge  are  always  practically  the 
same.  Hence  the  spring  is  called  a  periodical 
spring. 

The  cause  of  periodical  springs  is  due  to  the  siphon- 
shape  of  the  outlet  tube.  A  siphon  is  a  tube  so  bent  as  to 
have  two  vertical  arms  of  unequal  length.  When  filled, 
it  will  continue  to  discharge  as  long  as  its  shorter  arm  is 
below  the  water  and  the  longer  arm  free.  If  a  large  cav- 
ernous reservoir  be  in  connection  with  the  surface  of  the 
earth  by  a  tube  of  this  shape,  it  will  begin  to  discharge  its 
water  when,  by  infiltration,  the  level  reaches  the  highest 
bend  of  the  tube,  as  at  a,  in  Fig.  58,  since  the  water  will  then 
drive  out  the  air  and  fill  the  entire  tube.  The  discharge 
will  then  continue  until  the  water-level  falls  below  the 
mouth  of  the  tube,  or  at  6,  in  the  figure.  The  time  of  the 
discharge  is  always  practically  the  same,  since  the  same 
quantity  is  discharged  each  time  under  exactly  similar 
conditions. 

Springs  are  common  on  the  shores  of  the  ocean.  Their 
waters  are  fresh  because  the  outflow  of  the  fresh  water 
prevents  the  inflow  of  the  salt  water.  This  is  the  case 
even  on  coral  islands,  where  the  height  of  the  land  is 
but  ten  or  twelve  feet  above  the  sea.  A  comparatively 
shallow  well,  on  such  islands,  generally  yields  fresh  water, 
derived,  of  course,  from  the  rainfall. 

161.  Depth  of  Reservoir. — According  to  the 
distance  the  reservoir  is  situated  below  the  sur- 
face of  the  earth,  springs  are  divided  into  Cold, 
and  Hot  or  Thermal. 

Cold  Springs  are  those  whose  temperature  does 
not  exceed  60°  Fahr.  Their  waters  are  sometimes 
much  colder  than  60°  Fahr. 

Very  cold  springs  owe  their  low  temperatures 
to  the  sources  whence  they  draw  their  supplies. 
In  mountainous  districts  these  can  generally  be 
traced  to  the  melting  of  huge  snow-fields,  or 
masses  of  ice  called  glaciers.  The  temperature 
in  such  cases  is  often  nearly  that  of  ordinary  ice- 
water. 

The  reservoirs  of  all  springs  the  temperature 
of  whose  waters  ranges  from  50°  to  60°  are,  in 
general,  comparatively  near  the  surface.  They 
are  colder  than  surface  waters — 

(1.)  Because  they  are  shielded  from  the  sun ; 

(2.)  Because  evaporation  occurs  in  their  cav- 
ernous reservoirs. 

The  temperature  of  springs  of  this  kind  is,  in 
general,  but  slightly  affected  by  changes  in  the 
temperature  of  the  outer  air.  Since  the  reservoirs 
of  ordinary  springs  are  shielded  from  the  hot  air 
in  summer  and  from  the  cold  air  in  winter,  their 
waters  are  colder  than  river-water  in  summer,  and 
warmer  than  river-water  in  winter.  Their  waters 
average,  in  their  temperature,  that  of  the  strata 
over  which  they  flow  in  their  subterranean  course. 


DRAINAGE. 


61 


The  mean  annual  temperature  of  the  strata  over 
which  the  waters  flow  can,  therefore,  he  ascertained 
by  plunging  a  thermometer  into  the  water  as  it 
comes  out  of  the  spring. 

Hot  or  Thermal  Springs  range  in  temperature 
from  60°  Fahr.  to  the  boiling-point.  In  geysers 
the  temperature  of  the  water  far  down  in  the  tube 
is  considerably  above  the  boiling-point  at  the  sur- 
face. 

Hot  springs  which  occur  in  the  neighborhood 
of  active  volcanoes  owe  their  high  temperature  to 
the  vicinity  of  their  reservoir's  to  beds  of  recently- 
ejected  lava. 

Hot  springs,  however,  are  common  in  regions 
distant  from  volcanic  disturbance.  In  such  cases 
their  high  temperature  must  be  attributed  to  the  dis- 
tance of  their  reservoirs  from  the  earth's  surface,  the 
heat  being  derived  directly  from  the  interior. 

In  some  cases  the  source  of  the  heat  is  to  be  attributed 
to  chemical  action  in  neighboring  strata. 

Thermal  springs,  whose  reservoirs  are  at  comparatively 
moderate  depths,  may  discharge  their  waters  by  ordinary 
hydrostatic  pressure;  but  where,  from  the  great  depth  of 
the  reservoirs,  this  force  would  be  insufficient,  the  waters 
are  probably  raised  to  the  surface  by  the  pressure  of  super- 
heated steam  or  compressed  gas. 

Since  the  temperature  rises  1°  for  about  every  55  feet  of 
descent,  in  cases  where  the  increased  temperature  is  due 
solely  to  depth,  if  the  issuing  waters  have  a  tempera- 
ture of  149°  Fahr.,  the  reservoirs  must  be  about  one  mile 
below  the  surface,  or  fifty-five  times  the  difference  between 
149°  and  60°,  the  temperature  of  ordinary  springs.  In 
many  cases  the  waters  probably  rise  from  profound  depths 
as  columns  of  steam,  condensing  in  reservoirs  that  are  less 
profound. 

Source  of  Deep-seated  Waters. — Deep-seated  waters 
are  probably  derived  by  infiltration  from  the  bed  of  the 
ocean.  The  natural  porosity  of  large  areas  is  greatly  in- 
creased by  the  immense  pressure  of  the  water,  which  in 
the  deep  ocean  is  equal  to  thousands  of  pounds  per  square 
inch. 


Fig.  59.    Artesian  Well. 

162.  Artesian  Wells  differ  from  ordinary  wells 
in  that  their  waters  are  discharged  by  natural 


pressure  on  their  reservoirs,  so  that  pumping  is 
not  necessary  to  raise  the  water.  Such  wells  are 
therefore  true  springs. 

The  reservoirs  are  basin-shaped,  and  generally 
consist  of  several  water-logged,  porous  strata,  con- 
tained between  two,  curved,  impervious  strata.  If 
the  upper  porous  layer  be  pierced,  the  waters  will 
flow  out  by  reason  of  the  pressure  of  the  liquid 
in  the  higher  parts.  The  reservoirs  of  many 
natural  springs  are  of  this  kind,  the  upper  im- 
pervious strata  being  broken  in  one  or  more 
places  by  some  natural  force. 

Artesian  wells  have  been  sunk  to  great  depths,  and  it  is 
a  significant  fact  that  the  temperature  of  the  issuing 
waters  is  always  proportional  to  the  depth,  showing  a 
nearly  constant  increase  of  1°  above  the  temperature  of 
ordinary  springs — viz.  about  60°  Fahr. — for  every  55  feet 
of  descent.  In  the  case  of  the  artesian  well  of  Grenelle, 
Paris,  the  successful  boring  of  which  was  accomplished 
only  after  many  years  of  the  most  discouraging  labor, 
and  which  reached  a  depth  of  nearly  1800  feet,  the  tem- 
perature of  the  water  was  82°  Fahr.  A  well  at  Neusalz- 
werk,  Prussia,  has  penetrated  2200  feet;  its  temperature 
is  91°  Fahr. 

163.  Geysers  are  boiling  springs  which,  at  in- 
tervals more  or  less  regular,  shoot  out  huge  col- 
umns of  water  with  great  violence.     They  are 


Fig.  60.    Geyser  in  Eruption. 

confined  to  the  neighborhood  of  volcanic  dis- 
tricts, and,  by  some,  are  classed  with  subordinate 
volcanic  phenomena.      The  jets  of  water  some- 


62 


PHYSICAL    GEOGRAPHY. 


times  reach  a  height  of  more  than  two  hundred 
feet. 

The  geyser  issues  from  the  summit  of  a  conical  hillock 
of  silicious  material  deposited  by  the  water.  A  broad, 
shallow  basin  generally  surmounts  the  hillock  and  forms 
the  mouth  of  a  deep,  funnel-shaped  tube.  The  sides  of 
both  tube  and  basin  are  lined  with  a  smooth  incrustation 
of  silica.  In  the  Great  Geyser  of  Iceland,  the  basin  is  52 
feet  wide  and  the  tube  75  feet  deep. 

Both  the  tube  and  basin  are  the  work  of  the  spring, 
being  deposited  from  the  silica  contained  in  the  highly 
heated  waters.  It  is  only  when  the  tube  has  reached  a 
certain  depth  that  the  spring  becomes  a  true  geyser. 
When  the  depth  becomes  too  great  the  geyser  eruptions 
cease,  the  waters  forcing  their  way  through  the  walls  of 
the  tube  to  some  lower  level.  Hence,  in  all  geyser  re- 
gions, numerous  deserted  geyser-tubes,  and  simple  ther- 
mal springs  occur. 

The  waters  of  some  geyser  regions  are  calcareous.  In 
this  case  the  tube  of  the  geyser  is,  of  course,  formed  of 
limestone. 

164.  Bunsen's  Theory  of  Geysers. — Bunsen  explains 
the  cause  of  geyser  eruptions  as  follows :  The  heat  of  the 
volcanic  strata,  through  which  the  geyser-tube  extends, 
causes  the  water  which  fills  it  to  become  highly  heated. 
The  water  at  the  bottom  of  the  tube,  having  to  sustain 
the  pressure  of  that  above  it,  gradually  acquires  a  tem- 
perature far  above  the  boiling-point  at  the  surface.  The 
temperature  of  the  water  in  the  tube  will,  therefore,  de- 
crease from  the  bottom  to  the  surface. 

If  now,  when  the  tube  is  filled,  the  water,  near  the  mid- 
dle, is  brought  to  its  boiling  temperature,  the  steam  thus 
formed  momentarily  lifts  the  water  in  the  upper  part  of 
the  tube,  when  the  water  in  the  lower  part,  released  from 
its  pressure,  bursts  into  steam  and  forcibly  ejects  the  con- 
tents of  the  tube. 

Bunsen  succeeded  in  lowering  a  thermometer  into  the 
tube  of  the  Great  Geyser  in  Iceland  just  before  an  erup- 
tion. At  the  depth  of  72  feet  he  found  the  temperature 
of  the  water  to  be  261°  Fahr.,  or  49°  above  the  ordinary 
boiling-point. 

165.  Geyser  Regions. — There  are  three  exten- 
sive geyser  regions : 

(1.)  In  Iceland,  in  the  south-western  part  of 
the  island,  where  over  one  hundred  occur  in  a 
limited  area. 

(2.)  In  New  Zealand,  about  the  centre  of  the 
northern  island,  where,  near  the  active  volcano 
Tongariro,  over  one  thousand  mud  springs,  hot 
springs,  and  geysers  burst  from  the  ground. 

(3.)  In  Yellowstone  National  Park,  in  Wyoming, 
where  numerous  large  geysers  occur,  mostly  near 
the  head-waters  of  the  Madison  and  Yellowstone 
Rivers,  at  heights  often  as  great  as  8000  feet 
above  the  sea-level.  Here  the  boiling-point  of 
the  water  at  the  surface  of  the  geyser,  owing  to 
the  diminished  atmospheric  pressure,  is  as  low 
as  about  200°  Fahr. 

A  small  geyser  region  is  found  in  California, 
near  San  Francisco. 


166.  Nature  of  the  Mineral  Substances  form- 
ing the  Reservoir. — The  subterranean  waters  dis- 
solve various  mineral  matters  either  from  the 
strata  over  which  they  flow,  or  from  their  reser- 
voirs ;  this  is  especially  true  of  thermal  springs, 
owing  to  the  greater  solvent  powers  of  the  heated 
waters. 

The  waters  of  mineral  springs  generally  contain 
a  number  of  mineral  ingredients.  Mineral  springs 
are  divided  into  various  classes  according  to  the 
predominating  material. 

(1.)  Calcareous  Springs  are  those  whose  waters 
contain  lime  in  solution. 

Thermal  waters  charged  with  carbonic  acid  usually  con- 
tain large  quantities  of  lime,  which  they  have  dissolved 
from  subterranean  strata.  On  reaching  the  surface  the 
waters  cool  and  part  with  some  of  their  carbonic  acid,  and 
deposit  layer  after  layer  of  hard  limestone,  called  travertine. 
In  this  way  immense  quantities  of  limestone  are  brought 
to  the  surface  from  great  depths,  leaving  huge  subterra- 
nean caverns. 

In  portions  of  Tuscany,  Italy,  beds  of  travertine  occur 
more  than  250  feet  thick. 

(2.)  Silicious  Springs  are  those  whose  waters 
contain  silicon. 

(3.)  Sulphurous  Waters  are  those  whose  waters 
contain  sulphuretted  hydrogen  and  various  metal- 
lic sulphides  or  sulphates. 

Sulphurous  springs  are  found  in  Baden,  near  Vienna, 
and  in  Virginia. 

(4.)  Chalybeate  Waters  are  those  whose  waters 
contain  iron. 

(5.)  Brines,  or  those  whose  waters  contain  com- 
mon salt. 

The  springs  of  Halle,  in  the  Alps  of  Salzburg,  yield 
15,000  tons  of  salt 'annually.  The  artesian  well  of  Neu- 
salzwerk,  Prussia,  yields  about  28,000  tons  annually.  In 
the  United  States  the  springs  of  Salina  and  Syracuse  are 
among  the  most  important.  The  water  in  the  springs  of 
Salina  is  ten  times  Salter  than  ocean-water.  The  salt  is 
obtained  from  these  springs  by  the  evaporation  of  the 
water. 

(6.)  Acidulous  Springs  are  those  whose  waters 
contain  large  quantities  of  carbonic  acid  gas,  as 
the  Seltzer  springs  in  Germany,  and  those  of 
Vichy  in  France. 

167.  Petroleum  and  Bituminous  Springs. — Be- 
sides the  springs  above  mentioned,  there  are  two 
others,  closely  connected,  but  which  can  scarcely 
be  included  in  any  of  the  above  classes.  These 
are  petroleum  and  bituminous  springs. 

Petroleum  Springs  are  those  containing  rock-  or  coal- 
oil.  They  rise  from  large  reservoirs  containing  oil  instead 
of  water.  The  oil  is  derived  from  the  slow  decomposition, 
in  the  presence  of  heat,  of  various  animal  and  vegetable 


RIVERS. 


63 


matters  which  are  found  in  the  strata  of  nearly  all  the 
geological  formations.  The  reservoirs  are  of  the  same 
nature  as  those  of  artesian  wells,  the  oil  being  obtained 
by  boring. 

Petroleum  springs  are  numerous.  The  most  extensive 
regions  in  the  world  ai-e  found  in  the  great  oil  districts  of 
Western  Pennsylvania  and  the  neighboring  States. 

Bituminous  Springs,  or  those  from  which  pitch  or 
bitumen  issue.  Their  origin  is  the  same  as  that  of  oil 
springs,  the  decomposition,  however,  occurring  in  a  some- 
what different  way.  The  famous  pitch  lake  on  the  island 
of  Trinidad,  north-east  of  South  America,  probably  owes 
its  origin  to  the  large  quantities  of  trees  and  other  vege- 
table matters,  which  have  been  rolled  down  the  Orinoco 
and  buried  in  the  delta  formation  on  the  eastern  shores 
of  the  island. 


XJ^C 


CHAPTER   III. 
Rivers. 

168.  Definitions. — The  water  that  issues  from 
the  ground  as  springs,  that  is  derived  from  the 
melting  of  ice  or  snow,  or  that  drains  directly 
from  the  surface  after  rainfall,  runs  down  the 
slopes  of  the  land  and  collects  in  the  depressions 
formed  by  the  intersection  of  the  slopes,  forming 
rills  or  rivulets,  which  at  last  combine  in  larger 
streams  called  rivers. 

The  source  of  a  river  is  the  place  where  it 
rises ;  the  mouth,  the  place  where  it  empties ;  the 
channel,  the  depression  through  which  it  flows. 
Rivers  generally  rise  in  mountains,  where  the 
rainfall  is  greater  than  elsewhere,  and  where 
vast  beds  of  snow  and  ice  occur. 

In  reality,  all  rivers  have  three  mouths,  or  places  where 
they  discharge  their  waters : 

(1.)  Where  the  river  empties  directly  into  some  other 
body  of  water ; 

(2.)  Where  the  river  empties  by  evaporation  into  the 
air ;  that  is,  its  entire  upper  surface ; 

(3.)  Where  the  river  empties  into  the  earth  through  the 
porous  strata  of  its  bed  or  channel. 

Since  the  downward  motion  of  a  river  is  caused  by  the 
inclination  of  its  channel  from  the  source  to  the  mouth,  a 
correct  idea  of  the  general  inclination  of  any  country  can 
be  obtained  by  a  careful  study  of  a  map  in  which  the  di- 
rections of  the  rivers  are  represented.  In  studying  the 
various  river-systems  the  student  should  endeavor  to  ob- 
tain in  this  way  clear  ideas  of  the  general  directions  of  the 
tontinental  slopes. 

The  River-System  is  the  main  stream,  with  all 
its  tributaries  and  branches. 

The  Basin  is  the  entire  area  of  land  which 
drains  into  the  river-system. 

The  Water-shed  is  the  ridge  or  elevation  which 


separates  two  opposite  slopes.  The  streams  flow 
in  opposite  directions  from  the  water-shed. 

The  Velocity  of  a  river  depends  on  the  inclina- 
tion or  pitch  of  the  channel  and  the  volume  or 
depth  of  the  water. 

169.  River-Courses. — The  river-channel,  from 
its  source  to  its  mouth,  is,  for  ease  of  description, 
conveniently  divided  into  three  parts  or  courses : 
the  upper,  middle,  and  lower. 

The  Upper  Course  of  a  river  is  that  part  which 
is  situated  in  the  mountainous  or  hilly  country 
near  its  source.  In  this  course  the  river  has  a 
great  velocity,  and  its  channel  is  characterized  by 
sharp,  sudden  turns,  alternating  with  long,  straight 
courses.  In  the  upper  course  erosion  occurs 
almost  entirely  along  the  bottom  of  the  channel, 
so  that  the  river  runs  between  steep,  and  some- 
times almost  vertical,  banks.  In  this  way  river- 
valleys  are  formed,  generally  with  narrow  and 
overhanging,  precipitous  sides.  In  the  upper  and 
middle  courses  rapids  and  waterfalls  occur. 

Rapids  and  Waterfalls. — During  the  erosion  of 
the  channel,  where  harder  rocks  occur  in  the  bed 
of  the  stream,  the  softer  strata,  immediately  adjoin- 
ing them  down  stream,  are  rapidly  worn  away,  and 
the  obstruction  becomes  at  last  the  head  of  a 
waterfall.  The  height  grows  rapidly  from  the 
increased  force  of  the  falling  water,  and  continues 
until  stopped  by  some  similar  obstruction  below. 


\   5y    i     U 

i              i 

VH 

2                             2 

-^ 

3  3 

4  4 

Fig,  61.    Erosion  of  Waterfall. 

Thus,  suppose  a  a,  Fig.  61,  is  the  bed  of  a  river,  the  di- 
rection of  flow  of  which  is  shown  by  the  arrow.  The  softer 
rock  being  worn  away  more  rapidly,  the  bed  reaches  the 
level  1,  1.  A  fall,  and  consequent  increase  in  the  velocity 
of  the  river,  soon  causes  the  level  of  the  bed  to  reach  2,  2, 
3,  3,  and  4,  4,  successively.  At  the  same  time  the  falling 
water  eats  away  the  vertical  wall  of  the  precipice,  causing 
the  waterfall  to  move  up  stream.  The  water  then  cuts  the 
precipice  away  in  steps,  as  shown  at  5,  6,  7,  thus  changing 
the  fall  into  cascades.  These  are  finally  worn  away,  as 
shown  at  8,  changing  the  cascades  to  rapids,  when,  finally, 
the  fall  disappears  entirely,  or  the  erosion  of  the  hard 
rock  is  completed. 

When  the  water  falls  perpendicularly — that  is, 
when  it  does  not  slip  or  slide — it  forms  a  water- 
fall or  cataract;  in  all  other  cases  of  swift  de- 
scent it  forms  rapids. 


64 


PHYSICAL    GEOGRAPHY. 


Fig.  62.    The  Falls  of  Niagara. 

The  grandest  falls  in  the  world  are  those  of  the  Niagara, 
160  feet  high.  Though  greatly  inferior  to  many  others  in 
height,  yet  their  volume  of  water  is  so  great  that  they 
surpass  all  others  in  grandeur.  The  Victoria  Falls  of  the 
Zambezi  in  Africa  nearly  equal  in  volume  those  of  the 
Niagara.     Their  height  is  360  feet. 

The  highest  falls  in  the  world  are  those  of  the  Yosemite, 
in  California.  Two  projecting  ledges  break  the  sheet  into 
three  falls,  whose  total  height  exceeds  2000  feet.  One  of 
the  highest  falls  in  Europe  is  the  Staubbach  or  Dust-brook, 
in  the  valley  of  the  Lauterbriinnen  in  Switzerland.  The 
water  makes  one  sheer  fall  of  959  feet,  and  is  lost  in  a 
sheet  of  mist  before  it  reaches  the  ground. 

The  Middle  Course  extends  from  where  the 
river  emerges  from  the  mountainous  or  hilly  dis- 
tricts to  the  low  plains  near  the  mouth.  The 
descent  is  comparatively  slight,  and  the  velocity 
small.  The  erosion  of  the  bottom  of  the  channel 
is  insignificant,  but  at  the  sides,  especially  during 
freshets,  the  river  undermines  its  banks  and  thus 
widens  its  valley.  Here  the  river  is  divided  into 
two  distinct  portions :  the  channel  proper  and  the 
alluvial  flats  or  flood-grounds. 

The  Lower  Course  extends  from  the  middle 
course  to  the  mouth.  The  fall  is  slight,  and  the 
velocity  small. 

170.  Changes  in  River-courses. — During  floods,  when 
the  velocity  and  eroding  power  are  greatly  increased,  ex- 
tensive changes  often  occur  in  river-courses.  After  the 
floods  have  subsided  the  water  is  found  running  through 
new  channels,  its  old  ones  being  either  completely  filled 
with  deposits  of  mud,  or  occupied  by  slender  streams. 
Along  the  Mississippi  these  partially  deserted  channels 
are  called  bayous,  and,  in  places,  widen  out  into  large  lakes. 


(See  Fig.  63.)  The  Red  River  appears  to  have  formerly 
emptied  into  the  Mexican  Gulf  through  a  separate  chan- 
nel. In  the  basins  of  the  Amazon,  the  Ganges,  and  the 
Po,  the  old  deserted  channels  are  numerous  on  both  banks 
of  the  streams. 

171.  River  Mouths. — A  wide,  open  river-mouth 
is  called  an  Estuary;  the  accumulation  of  mud 
or  sand  which  occurs  in  the  mouths  of  certain 
rivers  is  called  a  Delta. 

172.  Inundations. — During  certain  seasons  of 
the  year,  the  amount  of  water  drained  into  the 
river-channel  is  greater  than  it  can  discharge ;  it 
then  overflows  its  banks  and  inundates  the  sur- 
rounding country. 

Inundations  of  rivers  are  caused — 

(1.)  By  excessive  rainfall ; 

(2.)  By  periodical  rains ; 

(3.)  By  the  melting  of  ice  and  snow. 

In  the  tropics,  where  the  rainfall  is  more  or 
less  periodical,  the  inundations  of  the  rivers  are 
also  periodical.  The  melting  of  the  ice  and  snow, 
which  occurs  regularly  at  the  beginning  of  the 
warm  weather,  also  causes  periodical  inundations. 
The  Nile  rises  annually  on  account  of  the  period- 
ical rainfall  of  its  upper  sources ;  the  Mississippi 
semi-annually,  once  from  the  melting  of  snow, 
and  once  from  the  winter  rainfall. 

When  both  the  area  of  the  river-basin  and  the  rainfall 
in  inches  are  known,  experience  permits  of  a  calculation, 
by  means  of  which  the  probable  time  and  extent  of  rise  of 
water  in  a  river  can  be  approximately  predicted.  In  times 
of  heavy  rainfall,  the  Weather  Bureau  of  the  United 
States  is  enabled  to  predict  the  probable  rise  of  the  im- 
portant rivers. 

Influence  of  the  Destruction  of  the  Forests  on  In- 
undations.— When  the  forests  are  removed  from  a  large 
portion  of  a  river-basin,  the  rains  are  no  longer  absorbed 
quietly  by  the  ground,  but  drain  rapidly  off  its  surface  into 
the  river-channels,  and  thus  in  a  short  time  the  entire 
precipitation  is  poured  into  the  main  channel,  causing  an 
overflow.  It  is  from  this  cause  that  the  disastrous  effects 
of  otherwise  harmless  storms  are  produced.  The  inunda- 
tions are  most  intensified  by  this  cause  in  the  early  spring, 
when  the  ice  and  snow  begin  to  melt.  The  destructive 
effects  of  the  floods  are  increased  by  masses  of  floating  ice, 
which,  becoming  gorged  in  shallow  places  in  the  stream, 
back  up  the  waters  above.  The  increased  frequency  of 
inundations  in  the  United  States  is,  to  a  great  extent,  to 
be  attributed  to  the  rapid  destruction  of  the  forests. 

173.  The  Quantity  of  Water  Discharged  by  a 
River  depends  principally — 

(1.)  On  the  size  of  the  basin  ; 
(2.)  On  the  amount  of  the  rainfall. 

The  quantity  of  water  in  a  river  also  depends — 
(1.)  On  the  climate  of  the  basin,  a  dry,  hot  air  diminish- 
ing the  quautity  by  evaporation ; 

(2.)  On  the  physical  features  of  the  basin,  whether  wooded 
or  open ; 


TRANSPORTING    POWER    OF    RIVERS. 


65 


(3.)  On  the  nature  of  the  bed  or  channel,  whether  leaky 
or  not. 

It  will  be  noticed  that  these  three  circumstances  are 
connected  with  the  two  additional  river-mouths  already 
alluded  to :  the  air-surface  of  the  river,  and  the  channel- 
surface. 

Keith  Johnston  estimates  the  daily  discharge  of  all  the 
rivers  of  the  world  at  229,000,000,000  cubic  yards,  or  over 
2,620,000  cubic  yards  per  second. 


x>XKc 


CHAPTER  IV. 

Transporting  Power  of  Rivers. 

174.  Silt  or  Detritus. — Rivers  are  ceaselessly 
at  work  carrying  the  eroded  materials,  called  silt 
or  detritus,  from  their  upper  to  their  lower  courses. 
Valleys  are  thus  formed,  miles  in  width  and  thou- 
sands of  feet  in  depth,  and  lofty  mountains  greatly 
reduced  in  height. 

The  amount  of  silt  transported  by  rivers  is  almost  in- 
credible. According  to  the  careful  estimates  of  Hum- 
phreys and  Abbot,  the  silt  brought  down  every  year  by 
the  Mississippi  and  thrown  into  the  Mexican  Gulf,  if 
collected  in  one  place,  would  cover  a  field  one  square  mile 
in  area  to  the  depth  of  268  feet.  According  to  Lyell,  the 
deposits,  in  the  Bay  of  Bengal,  of  the  Ganges  and  the 
Brahmapootra,  are  nearly  as  great. 

The  rivers  are  carrying  the  mountains  seaward, 
and  the  continents  are  thus  decreasing  in  mean 
height  and  increasing  in  mean  breadth. 

175.  Deposition  of  Silt. — Since  the  silt  or 
eroded  mineral  matter  is  heavier  than  water,  it 
will  settle  in  all  parts  of  the  river-course.  It  will, 
however,  remain  in  those  places  only  where  the 
velocity  of  the  river  is  comparatively  small. 
These  places  are  as  follows : 

(1.)  In  the  channel  of  the  river ; 
(2.)  On  the  banks,  over  the  alluvial  flats  or 
flood-grounds ; 

(3.)  At  the  mouth  ; 

(4.)  Along  the  coast  near  the  mouth. 

176.  In  the  Channel. — In  rivers  that  traverse 
great  plains,  the  inclination  near  the  mouth  is 
slight,  and  the  diminished  velocity  allows  the  ma- 
terial to  accumulate  in  the  channel,  thus  raising 
the  general  level  of  the  stream.  When  the  rivers 
traverse  settled  districts,  the  inhabitants  are  com- 
pelled to  erect  huge  river-walls  to  prevent  the 
flooding  of  the  adjacent  lands ;  and,  in  some  places, 
the  channel  has  beeu  filled  to  such  an  extent  that 
the  ordinary  level  of  the  river  is  higher  than  that 
of  the  plains  along  its  banks. 

The  levees  or  banks  of  the  Mississippi  are  of  this  nature. 
On  the  level  plain  of  Lombardy  the  surface  of  the  Po,  in 


some  places,  is  higher  than  the  tops  of  the  neighboring 
houses.  When  floods  occur  in  such  districts,  the  breaking 
of  a  levee  or  river-wall  is  generally  attended  by  much 
loss. 

177.  Rafts. — Drift  timber,  thrown  into  the  stream  by 
the  undermining  of  the  banks,  is  common  in  rivers  that 
traverse  wooded  districts.  Portions  of  such  timber,  be- 
coming imbedded  in  shallow  parts  of  the  channel,  form 
obstructions  which  prevent  the  passage  of  subsequent 
masses.  The  impediment  so  formed  checks  the  velocity 
of  the  stream,  and  mud  deposits  occur  between  the  trees. 
Such  accumulations  are  called  rafts.  The  raft  of  the  Bed 
Eiver,  previous  to  its  removal,  was  thirteen  miles  in  length. 
A  large  raft  exists  near  the  mouth  of  the  Mackenzie  Eiver 
in  British  America. 

178.  On  the  Alluvial  Flats  or  Flood-grounds. 

— The  low  flat  plains  on  the  sides  of  the  river, 
which  are  formed  by  the  erosion  of  the  banks  in 
the  middle  and  lower  courses,  are  covered  by  the 
water  when  the  river  overflows  its  banks.  In  the 
shallow  water  over  these  parts  the  velocity  of  the 
water  is  slight,  and  the  silt  is  deposited,  thus 
forming  rich  alluvial  plains. 

In  large  rivers  the  flood-grounds  often  attain  consider- 
able size.  In  the  Mississippi  at  Vicksburg  the  width  of 
the  alluvial  plain  is  over  60  miles. 

In  the  lower  courses  of  a  river,  the  velocity 
being  small,  comparatively  slight  obstacles  suffice 
to  turn  the  waters  from  their  course.  The  river- 
channel  is  therefore  characterized  by  wide  bends 


Fig,  63.    Alluvial  Plats  of  the  Mississippi, 
(Showing  deserted  courses  and  fluviatile  islands  and  lakes.) 

or  curves.  At  the  bend  of  a  river  the  main  cur- 
rent is  directed  against  one  of  the  banks,  where 
rapid  erosion  takes  place,  the  eroded  material  ac- 


cumulating  lower  down  the  river,  in  the  bed  of 

the  stream,  where  the  velocity  is  small.    The  river 

is  thus  continually  damming 

%k    'i^A        UP  portions  of  its  old  chan- 

X        %       nel  and  cutting  new  ones. 

The  rapid  excavation  of 
these  portions  of  the  alluvial 
plain  is  favored  by  the  loose 
materials  which  compose  it. 
Sometimes  the  river  cuts  a 
new  channel  across  the  nar- 
row neck  of  a  bend,  part  of 
its  waters  running  through 
the  old  channel  and  part 
through  the  new.  In  this 
way  jiuviatile  islands  are 
formed.  One  of  the  chan- 
nels is  sometimes  separated 
from  the  other  by  a  deposi- 
tion of  mud  or  sand.  The 
water  fills  the  old  channel 
by  soaking  through  the  soil, 
and  thus  Jiuviatile  lakes  are 
formed.  Numerous  fluviatile 
lakes  occur  near  the  banks  of  the  Lower  Missis- 
sippi and  the  Red  River. 


Fig,  64.  Formation  of 
Fluviatile  Islands  and 
Lakes. 


Thus,  suppose  the  river  flows  in  the  direction  of  the 
arrow  at  S,  Fig.  64,  and  its  channel  has  the  bends  shown. 
A  new  channel  may  be  formed  at  a,  b,  the  river  either 
flowing  through  both  channels,  thus  converting  the  neck 
of  land  I,  into  a  fluviatile  island,  or  the  old  channel  may 
fill  up  and  form  a  fluviatile  lake,  L,  by  bars  forming  in 
the  old  channel  at  a  and  b. 

179.  At  the  Mouth. — Delta  Formations.— In 

sheltered  parts  of  the  ocean,  where  the  tides  are 
weak  and  the  ocean-currents  feeble,  or  in  inland 
seas  and  lakes,  where  they  are  entirely  absent,  the 
eroded  material  accumulates  at  the  mouth  of  the 
river  in  large,  triangular-shaped  deposits,  called 
deltas,  from  their  resemblance  to  the  Greek  letter 
(J)  of  that  name. 

The  Delta  of  the  Mississippi  is  the  largest  in  the 
Western  Continent.  Its  entire  area  is  about  12,300  square 
miles,  though  but  two-thirds  of  it  are  permanently  above 
the  water,  the  remainder  being  a  sea-marsh.  It  begins  a 
little  below  the  mouth  of  the  Red  River.  The  stream  cuts 
through  the  delta  in  one  main  channel,  but  near  the  ex- 
treme end  of  the  delta  forms  several  mouths.  On  all  sides 
of  the  main  stream,  numerous  smaller  streams  force  their 
way  into  the  Gulf  through  the  soft  material. 

The  Delta  of  the  Nile,  at  its  outlet  into  the  Mediter- 
ranean, occupies  an  area  of  nearly  9000  square  miles.  A 
large  portion  of  the  sediment  of  the  river  is  deposited  over 
the  flood-grounds  during  inundations.  The  fertility  of  the 
land  is  largely  dependent  on  these  deposits. 


Fig.  65.    Delta  of  the  Mississippi.    (After  Dana.) 


The  Delta  of  the  Ganges  and  the  Brahmapootra, 
in  the  Bay  of  Bengal,  is  cousiderably  larger  than  the  Delta 
of  the  Nile.  Between  the  Hoogly  and  the  main  branch 
of  the  Ganges,  numerous  streams  force  their  way  between 
countless  islands,  called  the  Sunderbunds,  inhabited  by 
tigers  and  crocodiles.  The  Po,  the  Rhone,  the  Rhine,  and  the 
Danube  in  Europe,  the  Tigris,  the  Euphrates,  the  Yang-tse- 
Kiang  and  Hoang-Ho  in  Asia,  and  the  Senegal  and  the  Zam- 
besi in  Africa,  have  extensive  deltas. 


180.  Along  the  Coast,  near  the  Mouth. — Fluvio- 
Marine  Formations  are  deposits  of  silt  that  form 
along  the  coast  near  and  opposite  the  mouths  of 
rivers,  under  the  combined  action  of  the  river- 
current  and  the  tides  of  the  ocean.  A  sand-bar 
is  formed  at  some  little  distance  from  the  mouth 
of  the  river,  where  the  outflowing  river-current 


DRAINAGE    SYSTEMS. 


67 


Fig.  66.    Fluvio- Marine  Formations. 

and  the  inflowing  tide  neutralize  each  other.  The 
impediment  so  formed  permits  of  the  rapid  de- 
position of  silt,  which  fills  up  the  portions  of  the 
ocean  so  shut  off,  and  converts  them  into  shallow 
bodies  of  water  called  sounds.  These  sounds,  by 
gradual  rising  of  the  land,  are  afterward  con- 
verted into  river-swamps.  According  to  Dana, 
the  eastern  and  southern  coasts  of  the  United 
States,  from  Virginia  to  Texas,  are  an  almost  con- 
tinuous fluvio-marine  formation.  Albemarle  and 
Pamlico  Sounds  and  the  Great  Dismal,  Alligator, 
and  Okefinoke  Swamps  are  but  different  stages  in 
the  formation  of  these  deposits. 


CHAPTER  V. 
Drainage  Systems. 

181.  Continental  Drainage  is  dependent  on  the 
position  of  the  mountain-systems  and  the  direc- 
tion of  their  slopes.  The  mountain-ridges  or 
peaks,  or  the  high  plateaus,  form  the  water-sheds. 
In  some  cases,  from  a  single  peak  or  plateau,  the 
water  drains  into  distinct  river-systems,  emptying 
into  different  oceans. 

182.  North  America. — The  central  plain  of 
North  America  is  drained  by  four  large  river- 
systems  :  the  Mackenzie  into  the  Arctic  Ocean ; 
the  Saskatchewan  and  the  Nelson  into  Hudson 
Bay ;  the  St.  Lawrence  into  the  Gulf  of  St.  Law- 


rence ;  and  the  Mississippi  into  the  Gulf  of  Mex- 
ico. The  basin  of  the  Mississippi  occupies  the 
long  slopes  of  the  Rocky  Mountains  and  the 
Appalachians.  The  Missouri  and  the  Ohio  are 
the  principal  tributaries  of  the  Mississippi. 

Numerous  streams  descend  the  eastern  slopes 
of  the  Appalachian  system  into  the  Atlantic. 

Owing  to  the  position  of  the  predominant  sys- 
tem, the  streams  which  empty  into  the  Pacific  are 
comparatively  small.  The  principal  are  the  Yu- 
kon, the  Columbia,  and  the  Colorado. 

There  are  several  remarkable  isolated  water-sheds  or 
drainage-centres  in  North  America.     These  are — 

(1.)  In  the  central  part  of  the  Rocky  Mountain  system, 
where  the  land  drains  in  different  directions  into  the  sys- 
tems of  the  Mississippi,  the  Columbia,  and  the  Colorado 
Rivers. 

(2.)  In  the  northern  part  of  the  Rocky  Mountains, 
where  the  drainage  is  received  by  the  systems  of  the 
Yukon,  the  Mackenzie,  and  the  Saskatchewan  Rivers. 

183.  South  America  resembles  North  America 
in  its  drainage  systems.  The  long,  gentle  slopes 
of  the  Andes,  and  those  of  the  systems  of  Brazil 
and  of  Guiana,  are  occupied  at  their  intersections 
by  the  three  great  river-systems  of  the  continent : 
that  of  the  Orinoco,  in  the  north  ;  that  of  the 
Amazon,  near  the  centre;  and  that  of  the  La 
Plata,  in  the  south.  Nearly  the  entire  continent 
is  drained  by  these  rivers  and  their  tributaries 
into  the  basin  of  the  Atlantic. 

The  Pacific  receives  no  considerable  streams. 
Only  impetuous  mountain-torrents  are  found. 

The  Magdalena,  which  drains  north,  corresponds  to  the 
Mackenzie;  the  Orinoco  and  the  Amazon,  which  drain 
east,  to  the  Nelson  and  the  St.  Lawrence;  and  the  La 
Platte,  which  drains  south,  to  the  Mississippi. 

184.  Europe  forms  an  exception  to  the  other 
continents  as  regards  its  drainage.  Though  some 
of  its  large  rivers  rise  in  its  predominant  moun- 
tain-system, yet  the  majority  rise  in  the  incon- 
s \terable  elevations  of  the  Valdai  Hills.  The 
Alps  are  drained  by  four  large  rivers — the  Phone, 
the  Rhine,  the  Danube,  and  the  Po.  These  all 
have  large  deltas. 

Although  in  this  part  of  the  continent  the  frequent  in- 
tersection of  the  two  lines  of  trend  produces  numerous 
basin-shaped  valleys,  yet,  owing  to  breaks  in  the  enclosing 
mountains,  none  of  any  size  have  an  inland  drainage,  but 
discharge  their  waters  through  numerous  tributaries  into 
one  or  another  of  the  principal  river-systems. 

The  Great  Low  Plain  of  Europe  is  drained 
toward  the  north  and  west  by  the  Petchora  and 
Dwina  into  the  Arctic ;  by  the  Duna,  the  Nie- 
men,  the  Vistida,  and  the  Oder  into  the  Baltic; 


Page.  6(9. 


LAKES. 


69 


and  by  the  Elbe  and  the  Weser  into  the  North 
Sea.  It  is  drained  toward  the  south  and  east  by 
the  Ural  and  the  Volga  into  the  inland  basin  of 
the  Caspian ;  and  by  the  Don,  the  Dnieper,  and 
the  Dniester  into  the  Sea  of  Azov  and  the  Black 
Sea. 

All  the  peninsulas  have  streams  traversing  them.  The 
Seine,  the  Loire,  and  the  Garonne  from  France,  and  the 
Douro,  the  Tagus,  and  the  Gaudiana  from  Spain  and  Por- 
tugal, empty  into  the  Atlantic.  The  Ebro  from  Spain, 
and  the  Po  from  Italy,  empty  into  the  Mediterranean. 

185.  Asia  possesses  the  most  extensive  inland 
drainage  of  all  the  continents.  The  plateaus  are 
surrounded  by  lofty  mountains  containing  but 
comparatively  few  breaks,  and  their  waters,  there- 
fore, can  find  no  passage  to  the  sea.  The  outer 
slopes,  however,  are  drained  by  some  of  the 
largest  rivers  in  the  world. 

The  Great  Northern  Plain  drains  into  the 
Arctic,  mainly  through  the  Lena,  the  Yenisei, 
and  the  Obe. 

The  Eastern  Slopes  drain  into  the  Pacific 
through  the  Amoor,  the  Hoang-Ho,  the  Yang-tse- 
Kiang,  and  the  Cambodia. 

The  Southern  Slopes  drain  into  the  Indian 
Ocean  through  the  Irrawaddy,  the  Brahmapootra, 
the  Ganges,  the  Indus,  the  Tigris,  and  the  Eu- 
phrates. 

The  principal  drainage-centre  in  Asia  is  the  Plateau  of 
Thibet,  from  which  descend  the  Hoang-Ho,  the  Yang-tse- 
Kiang,  the  Cambodia,  the  Irrawaddy,  the  Ganges,  the 
Brahmapootra,  and  the  Indus. 

186.  Africa,  being  low  in  the  interior,  with 
high  mountain-walls  on  her  borders,  is  charac- 
terized, like  the  Americas,  by  the  union  of  her 
smaller  river-systems  into  a  few  large  streams, 
which  drain  nearly  the  entire  continent.  These 
embrace  the  Nile,  emptying  into  the  Mediterra- 
nean ;  the  Zambezi,  into  the  Indian  Ocean ;  and 
the  Orange,  the  Congo,  the  Niger,  and  the  Senegal, 
into  the  Atlantic. 

187.  Australia. — The  Murray,  which  drains  the 
south-eastern  part  of  the  continent  into  the  Indian 
Ocean,  is  the  only  considerable  stream. 

188.  Principal  Oceanic  Systems. — A  careful 
study  of  the  river-basins  of  the  different  oceans 
discloses  the  following  fact: 

The  Atlantic  and  Arctic  Oceans  receive  the 
waters  of  nearly  all  the  large  river-systems  of  the 
world. 

The  cause  of  this  is  as  follows :  The  predomi- 
nant systems  being  situated  nearest  the  deepest 
ocean,  the  long,  gentle  slopes  descend  toward  the 
9 


smaller,  shallower  oceans  (the  Atlantic  and  the 
Arctic),  which  thus  receive  the  greatest  drainage. 

For  details  of  the  various  river-systems — such  as  the 
length,  area  of  basin,  etc. — see  Table,  page  170. 


D^C 


CHAPTER  VI. 
Lakes. 

189.  Lakes  are  bodies  of  water  accumulated  in 
depressions  of  the  surface  of  the  land. 

They  are  connected  either  with  the  systems  of 
oceanic  or  of  inland  drainage.  The  waters  of 
lakes  draining  into  the  ocean  are  fresh;  those 
having  no  connection  with  the  ocean  are  salt. 

Depth. — From  their  mode  of  formation  lakes 
which  occur  in  mountainous  districts  are,  as  a 
class,  deeper  than  those  found  on  the  great  low 
plains,  since  the  former  occupy  the  basins  of  nar- 
row but  deep  valleys,  and  the  latter  the  depres- 
sions of  the  gentle  undulations  of  the  plain. 

In  mountainous  districts  the  depths  of  the  depressions 
are  sometimes  so  great  that  the  bottom  of  the  lake  is  con- 
siderably below  the  sea-level.  Lake  Maggiore  in  the  Swiss 
Alps  extends  about  2000  feet  below  the  level  of  the  sea. 


Lake  Superior. 


Lake  Huron. 


Fig.  67.    Elevations  and  Depressions  of  Lakes, 

One  of  the  most  remarkable  series  of  depressions  in  the 
general  land-surface  of  the  world  is  that  occupied  by  the 
waters  of  Lakes  Superior,  Michigan,  Huron,  Erie,  and  On- 
tario. Superior  and  Huron,  though  some  600  feet  above 
the  level  of  the  ocean,  reach,  in  their  greatest  depths,  far 
below  its  surface ;  the  former  being  270  feet,  and  the  latter 
about  400  feet,  below  the  general  level  of  the  Atlantic. 

When  a  lake  is  connected  with  a  river-system, 
the  place  where  the  principal  stream  enters  is 
called  the  head  of  the  lake ;  the  place  where  it 
empties  is  called  the  foot  of  the  lake. 

190.  Geographical   Distribution.  —  The  large 


70 


PHYSICAL    GEOGRAPHY. 


lake-regions   of   the   world   are   almost   entirely 
confined  to  the  northern  continents. 

191.  Oceanic  Drainage  Systems. — North  Amer- 
ica contains  the  most  extensive  lake-system  in  the 
world.  The  lake-region  surrounds  Hudson  Bay, 
and  drains  into  the  Arctic  through  the  Mac- 
kenzie; into  Hudson  Bay  through  the  Sas- 
katchewan ;  or  into  the  Atlantic  through  the 
St.  Lawrence.  To  it  belong  the  Great  Lakes — 
Superior,  Michigan,  Huron,  Erie,  and  Ontario — 


Fig.  68.    View  on  Lake  George,  N.  T. 

embracing  a  combined  area  of  nearly  100,000 
square  miles — and  the  numerous  lakes  of  Brit- 
ish America'. 

Athabasca,  Great  Slave,  and  Great  Bear  Lakes  drain 
into  the  Arctic  through  the  Mackenzie ;  Lake  Winnepeg, 
into  Hudson  Bay  through  the  Nelson ;  and  the  Great 
Lakes,  into  the  Atlantic  through  the  St.  Lawrence. 

Europe  contains  two  extensive  systems  of  fresh- 
water lakes.  The  larger  region  is  in  Low  Europe, 
and  surrounds  the  Baltic  Sea  and  its  branches ; 
to  it  belong  Lakes  Ladoga  and  Onega  in  Russia, 
Wener  and  Wetter  in  Sweden,  with  numerous 
smaller  lakes.  The  smaller  region  is  found  in 
the  Alps  in  High  Europe. 

Africa  contains  an  extensive  system  of  lakes 
west  of  the  predominant  system.  Victoria  and 
Albert  Nyanzas,  which  drain  into  the  Nile,  Lake 
Tanganyika,  which  drains  into  the  Livingstone 


or  the  Congo,  and  Lake  Nyassa,  which  drains 
into  the  Zambezi,  are  the  principal  lakes. 

The  remaining  continents  contain  but  few  large 
fresh-water  lakes.  In  South  America  we  find  Lake 
Maracaybo,  with  brackish  water  from  its  vicinity 
to  the  sea ;  and  in  Asia,  Lake  Baikal. 

192.  The  Inland  Drainage  Systems  are  inti- 
mately connected  with  that  of  inland  rivers.  The 
term  Steppe  Lakes  and  Rivers  is  generally  applied 
to  those  which  have  no  outlet  to  the  ocean. 

Cause  of  the  Saltness  of  Inland  Waters.— All  river- 
water  contains  a  small  quantity  of  common  salt  and  other 
saline  substances.  Since  lakes  which  have  no  outlet,  or, 
as  they  are  generally  called,  inland  lakes,  lose  their  waters 
by  evaporation  only,  the  saline  ingredients  must  be  con- 
tinually increasing  in  quantity;  the  water  of  such  lakes 
is  therefore  generally  salt. 

The  Dead  Sea  in  Syria  is  remarkable  for  the  quantity 
of  its  saline  ingredients.  In  every  one  hundred  pounds 
of  its  waters  there  are  over  twenty-six  pounds,  or  more 
than  one-fourth,  of  various  saline  ingredients. 

North  America. — The  largest  inland  drainage- 
system  is  in  the  Great  Basin,  containing  Great 
Salt,  Walker,  Pyramid,  and  Owen  Lakes. 

South  America. — The  largest  region  of  inland 
drainage  includes  the  plateau  of  Bolivia,  contain- 
ing Lake  Titicaca.  The  waters  of  this  lake  are 
fresh,  but  have  no  outlet  to  the  sea,  the  river  form- 
ing the  outlet  being  lost  in  a  salty,  sandy  plain. 

Europe  and  Asia  contain  a  vast  region  of  in- 
land drainage  extending  from  the  Valdai  Hills 
eastward  to  the  Great  Kinghan  Mountains,  em- 
bracing most  of  the  Asiatic  plateaus. 

The  region  contains  Lake  Elton  in  Bussia,  and  the  Cas- 
pian and  Aral  Seas.  The  combined  area  of  the  last  two 
is  175,000  square  miles.  They  receive  the  waters  of  the 
Volga,  the  Ural,  the  Sir,  and  the  Amoo,  all  large  streams. 
Numerous  lakes  occur  on  the  plateaus.  Lake  Lop,  in  the 
depression  north  of  Thibet,  receives  the  Tarim,  and  Lake 
Hamoon,  on  the  Iranian  plateau,  the  Helmund  Biver. 

Africa  contains  Lake  Tchad  in  the  Soudan,  re- 
ceiving the  Komadagu  and  the  Shirwa,  and  Lake 
Ngami  in  Southern  Africa. 

Australia  contains  Lakes  Eyre,  Torrens,  Gaird- 
ner,  and  Amadeo  near  the  southern  coast. 

193.  Utility  of  Lakes. — By  offering  extended  basins 
into  which  the  rivers,  when  swollen,  can  disgorge  them- 
selves, lakes  greatly  diminish  the  destructive  effects  of 
inundations,  often  checking  them  entirely.  They  afford 
extended  surfaces  for  evaporation,  and,  collecting  the  finer 
sediment  of  the  rivers  when  deserted  by  their  waters, 
form  fertile  plains. 


SYLLABUS. 


Water  is  formed  by  the  union  of  oxygen  and  hydrogen. 
The  waters  of  the  earth  may  be  divided  into  two  classes 
— the  continental  and  the  oceanic. 

Water  is  a  solid  at  and  below  32°  Fahr.,  a  liquid  from 
32°  to  212°,  and  a  vapor  above  212°.  It  passes  off  as  vapor, 
however,  at  all  temperatures. 

A  pint  of  water  is  heaviest  at  the  temperature  of  39.2° 
Fahr.  Hence  in  deep  lakes,  covered  with  ice,  the  lower 
layers  of  water  are  7.2°  Fahr.  above  the  freezing-point. 
Large  bodies  of  water  moderate  the  extremes  of  tem- 
perature, because  water  takes  in  more  heat  while  warming 
and  gives  out  more  on  cooling  than  any  other  common 
substance. 

During  the  freezing  of  a  body  of  water,  or  the  condensa- 
tion of  a  mass  of  vapor,  considerable  stored  heat-energy 
appears,  or  latent  heat  becomes  sensible  and  warms  the 
surrounding  air. 

After  a  body  of  water  has  been  cooled  to  the  tempera- 
ture of  32°  Fahr.,  it  has  still  142  heat-units,  or  pound-de- 
grees, to  lose  before  it  can  turn  into  ice. 

After  a  body  of  ice  has  been  warmed  to  the  temperature 
of  32°  Fahr.,^t  has  still  142  heat-units,  or  pound-degrees, 
of  heat  to  gain  before  it  can  turn  into  water. 

Therefore,  both  freezing  and  melting  are  gradual  pro- 
cesses. 

The  rains  cleanse  the  surface  of  the  earth  and  purify 
the  atmosphere. 

Water  is  necessary  for  the  existence  of  life.  It  forms 
the  main  food  of  both  animals  and  plants. 

The  atmospheric  waters  are  drained  into  the  ocean 
either  by  surface  or  subterranean  drainage. 

Springs  are  the  outpourings  of  the  subterranean  waters. 

Springs  may  be  classified  according  to  peculiarities  in 

the  size,  shape,  and  depth  of  their  reservoirs,  and  the 

nature  of  the  mineral  substances  composing  the  strata 

over  which  the  waters  flow  or  in  which  they  collect. 

According  to  the  size  of  their  reservoirs,  springs  are 
either  constant  or  temporary. 

If  their  reservoirs  have  siphon-shaped  outlet  tubes, 
their  discharges  are  periodical. 

When  their  reservoirs  are  superficial,  springs  are  cold; 
when  deep-seated,  they  are  hot  or  thermal. 

Springs  whose  waters  are  moderately  cold  have  their 
reservoirs  near  the  surface.  Their  lower  temperature  is 
due  to  their  waters  being  shielded  from  the  sun. 

Springs  with  very  cold  waters  have  their  sources  in  the 
melting  of  large  masses  of  ice  or  snow. 

Hot  or  thermal  springs  owe  their  high  temperature  to 
the  heat  they  receive  from  the  interior  of  the  earth. 

Geysers  are  boiling  springs,  which,  at  irregular  intervals, 
shoot  out  huge  columns  of  water  with  great  violence. 

The  most  extensive  geyser  regions  are  those  of  Iceland, 
New  Zealand,  and  Wyoming. 

Calcareous  springs  contain  lime;  silicious,  silex;  sul- 
phurous, sulphuretted  hydrogen  and  metallic  sulphides  or 
sulphates ;  chalybeate,  iron ;  brines,  common  salt ;  acidu- 
lous, carbonic  acid  ;  petroleum,  coal  oil ;  bituminous,  pitch. 
Eivers  are  fed  both  by  surface  and  subterranean  drain- 
age. 

The  main  stream  with  all  its  tributaries  and  branches 
is  called  the  river-system.  The  territory  drained  into  the 
river-system  is  called  the  river-basin.  The  ridge  or  ele- 
vation separating  opposite  slopes  is  called  the  water-shed. 


In  the  upper  courses  of  rivers  erosion  occurs  mainly  on 
the  bottom  of  the  channel ;  in  the  lower  courses,  at  the 
sides. 

In  the  lower  courses  of  rivers  extensive  flats  or  plains 
are  found.  They  are  caused  by  the  erosion  of  the  banks 
and  the  subsequent  deposition  of  fine  mud  during  inunda- 
tions. 

Eivers  are  constantly  at  work  carrying  the  mountains 
toward  the  sea.  Through  their  agency  the  mean  height 
of  the  continents  is  decreasing,  and  their  mean  breadth 
increasing. 

The  eroded  material,  or  silt,  may  accumulate — 1.  In  the 
channel  of  the  river;  2.  Along  the  banks,  on  the  alluvial 
flats  or  flood-grounds;  3.  At  the  river's  mouth;  and  4. 
Aloug  the  coast,  near  the  mouth. 

The  accumulations  in  the  channel  of  the  lower  Missis- 
sippi have  so  raised  the  bed  of  the  stream  as  to  necessitate 
the  erection  of  levees  or  embankments  along  the  sides. 

Where  the  tides  are  weak  and  the  ocean  currents  absent 
or  feeble,  the  eroded  material,  or  silt,  accumulates  at  the 
mouths  of  rivers  in  masses  termed  deltas. 

The  Alps  are  drained  by  the  Rhine,  the  Rhone,  the  Po, 
and  the  Danube ;  these  rivers  have  extensive  delta-forma- 
tions. 

The  plateau  of  Thibet  is  drained  by  the  Hoang-Ho,  the 
Yang-tse-Kiang,  the  Ganges,  the  Brahmapootra,  and  the 
Indus ;  all  these  rivers  have  extensive  delta-formations. 

Among  other  extensive  deltas  are  those  of  the  Missis- 
sippi, which  drains  the  long  slopes  of  the  Pacific  and 
Appalachian  mountain-systems;  the  Nile,  the  Tigris,  the 
Euphrates,  and  the  Zambezi. 

Fluvio-marine  formations  occur  along  the  coasts ;  they 
are  caused  by  the  combined  action  of  the  river  and  tides. 

The  destruction  of  forests,  by  increasing  the  rapidity  of 
drainage,  increases  the  violence  of  floods.  Lakes  along 
the  river-courses  decrease  their  violence,  by  allowing  the 
torrents  to  discharge  their  waters. 

The  direction  of  the  drainage  of  a  country  is  dependent 
on  the  direction  of  its  slopes. 

The  central  plain  of  North  America  is  drained  north 
into  the  Arctic  Ocean  through  the  Mackenzie ;  east  into 
the  Atlantic  through  the  Nelson  and  the  St.  Lawrence; 
and  south  into  the  Gulf  of  Mexico  through  the  Mississippi. 

The  central  plain  of  South  America  is  drained  north 
into  the  Caribbean  Sea  through  the  Magdalena,  east,  into 
the  Atlantic  through  the  Orinoco  and  the  Amazon,  and 
south,  into  the  Atlantic  through  the  Rio  de  la  Plata. 

The  rivers  draining  the  great  low  plain  of  Europe  rise 
either  in  the  Valdai  Hills  or  on  the  northern  slopes  of  the 
predominant  system. 

Asia  possesses  the  most  extended  system  of  inland 
drainage  of  the  continents.  Extended  systems  are  also 
found  in  North  America  and  Europe. 

The  Atlantic  and  the  Arctic  Oceans  drain  about  three- 
fourths  of  the  continental  waters. 

The  largest  systems  of  fresh-water  lakes  occur  in  North 
America  and  Europe. 

The  Great  Lakes  of  North  America  occupy  remarkable 
depressions  in  the  continent.  The  beds  of  some  of  them 
are  several  hundred  feet  below  the  level  of  the  sea. 

Lakes  without  an  outlet  are  salt,  because  the  waters 
they  receive  contain  small  quantities  of  saline  ingredients, 
while  the  waters  they  lose  contain  none. 


72 


PHYSICAL    GEOGRAPHY. 


REVIEW   QUESTIONS. 


What  is  the  composition  of  water  ? 

Enumerate  the  physical  properties  which  enable  water 
to  play  so  important  a  part  in  the  economy  of  the  earth. 

What  effect  has  the  temperature  of  the  maximum  den- 
sity of  water  on  the  freezing  of  large  bodies  of  fresh  water  ? 
Why? 

How  do  large  bodies  of  water  moderate  the  extremes  of 
heat  and  cold  ? 

Why  are  freezing  and  melting  necessarily  gradual  pro- 
cesses ? 

What  effect  has  a  heavy  rainfall  on  the  temperature  of 
the  atmosphere? 

Explain  the  cause  of  deserts. 

Define  subterranean  drainage.    Surface  drainage. 

Upon  what  does  the  quantity  of  water  discharged  by  a 
spring  in  a  given  time  depend? 

Explain  the  cause  of  periodical  springs. 

What  is  the  temperature  of  cold  springs?  Of  hot  or 
thermal  springs? 

What  is  the  probable  cause  of  the  high  temperature  of 
hot  springs? 

How  can  the  probable  depth  of  the  reservoir  of  an  arte- 
sian spring  be  ascertained  from  the  temperature  of  its 
waters  ? 

What  are  geysers?  Explain  the  cause  of  their  erup- 
tion. 

What  is  the  origin  of  the  tube  and  basin  of  the  geyser  ? 

Name  the  three  largest  geyser  regions  of  the  world. 

What  is  travertine ?    How  is  it  formed? 


Name  some  of  the  most  important  springs  from  which 
large  quantities  of  salt  are  obtained. 

What  is  believed  to  be  the  origin  of  petroleum  or  coal 
oil? 

How  are  the  precipices  of  waterfalls  caused?  In  what 
courses  of  a  river  are  they  most  common? 

Name  the  highest  waterfall  in  the  world.  The  grand- 
est. 

Distinguish  between  an  estuary  and  a  delta. 

How  does  the  destruction  of  the  forest  increase  the 
severity  of  inundations? 

Upon  what  does  the  quantity  of  water  in  a  river  de- 
pend? 

In  what  different  portions  of  a  stream  may  the  silt  or 
detritus  be  deposited? 

What  are  rafts  ?    How  are  they  caused  ? 

Explain  the  formation  of  fluviatile  islands  and  lakes. 

Name  some  of  the  most  extensive  delta-formations  in 
North  America.     In  Europe.     In  Asia.     In  Africa. 

What  is  the  probable  origin  of  the  swamp-lands  of  the 
Atlantic  seaboard? 

How  may  a  tolerably  accurate  notion  of  the  direction 
of  the  slopes  of  a  country  be  obtained  by  a  study  of  the 
direction  of  its  rivers? 

In  what  respects  do  the  drainage  of  North  and  South 
America  resemble  each  other? 

Name  the  principal  systems  of  inland  drainage  of  the 
world. 

Explain  the  cause  of  the  saltness  of  inland  waters. 


MAP  QUESTIONS. 


«&Kc 


Which  ocean  drains  the  largest  areas  of  the  continents  ? 
Which  the  smallest  ? 

Name  the  important  rivers  which  drain  into  the  Atlan- 
tic from  North  America.  From  South  America.  From 
Europe.     From  Africa. 

Name  the  important  rivers  which  drain  into  the  Pacific 
from  North  America.    From  Asia. 

Name  the  important  rivers  which  drain  into  the  Indian 
Ocean  from  Africa.    From  Asia.    From  Australia. 

What  two  systems  of  inland  drainage  are  there  in  North 
America  ?    What  large  region  in  South  America  ? 

Name  an  important  steppe  lake  and  river  in  each  of  the 
continents. 

Describe  the  region  of  inland  drainage  of  Europe  and 
Asia.    What  large  lakes  and  rivers  belong  to  this  region? 


Describe  the  regions  of  inland  drainage  of  Africa.  Of 
Australia.  Name  the  important  lakes  found  in  each 
region. 

What  South  American  river  corresponds  in  the  direction 
of  its  drainage  with  the  St.  Lawrence?  With  the  Mac- 
kenzie?   With  the  Mississippi? 

Name  the  large  rivers  which  drain  the  predominant 
mountain-system  of  Asia.  Of  Europe.  Of  Africa.  Of 
North  America.    Of  South  America.    Of  Australia. 

Describe  the  fresh-water  lake-region  of  North  America. 
Of  South  America.    Of  Europe.    Of  Africa. 

In  which  line  of  trend  are  most  of  the  fresh-water  lakes 
of  North  America  found  ? 

Name  the  Atlantic  rivers  which  have  large  deltas  The 
Pacific  rivers.    The  Indian  rivers. 


Section  II. 

OCEANIC    WATERS. 


-oXKc 


CHAPTER   I. 

The  Ocean. 

194.  Composition. — The  water  of  the  ocean 
contains  a  number  of  various  saline  ingredients, 
which  give  it  a  bitter  taste  and  render  it  heavier 
than  fresh  water  in  the  proportion  of  1.027  to  1. 

Every  hundred  pounds  of  ocean-water  contains 
about  three  and  one-third  pounds  of  various 
saline  ingredients. 

Chloride  of  sodiu»a,  or  common  salt,  chloride  of  magne- 
sium, sulphates  and  carbonates  of  lime,  magnesia,  and 
potassa,  and  various  bromides,  chlorides,  and  iodides,  are 
the  principal  saline  ingredients. 

195.  Origin  of  the  Saltness  of  the  Ocean. — The 
rivers  are  constantly  dissolving  from  their  channels  large 
quantities  of  mineral  matters,  and  pouring  them  into  the 
ocean.  Besides  this,  fully  three-fourths  of  the  earth's  sur- 
face is  covered  permanently  by  the  oceanic  waters.  In 
this  way  immense  quantities  of  mineral  ingredients  have 
been  dissolved  out  from  the  crust.  The  latter  cause  was 
especially  active  during  the  geological  past,  when  frequent 
convulsions  brought  fresh  portions  of  the  crust  into  con- 
tact with  the  warm  waters. 

The  ocean  is  salter  in  those  parts  where  the  evaporation 
exceeds  the  rainfall,  or  at  about  the  latitude  of  the  tropics; 
where  the  rainfall  exceeds  the  evaporation,  the  water  is 
slightly  fresher  than  at  the  equator. 

In  inland  seas,  like  the  Mediterranean  or  the  Red  Sea, 
which,  though  connected  with  the  ocean,  yet  lose  much 
more  of  their  waters  by  evaporation  than  by  outflow,  the 
proportion  of  salt  is  slightly  greater  than  in  the  ocean. 
In  such  cases  a  current  generally  flows  into  the  sea  from 
the  ocean.  In  colder  latitudes,  inland  seas,  like  the  Bal- 
tic, receiving  the  waters  of  large  rivers,  contain  rather 
less  salt  than  the  open  sea,  and  a  current  generally  flows 
from  them  into  the  ocean. 

196.  Color. — Though  transparent  and  colorless 
in  small  quantities,  yet  in  large  masses  the  color 
of  sea-water  is  a  deep  blue.  The  same  is  true 
of  fresh  water.  Over  limited  portions  of  the 
ocean  the  waters  are  sometimes  of  a  reddish  or 
a  greenish  hue,  from  the  presence  of  numberless 
minute  organisms. 

Sometimes  a  pale  light  or  phosphorescence, 
visible  only  at  night,  and  due  to  the  presence  of 
animalcule,  appears  where  the  air  comes  into  con- 
tact with  the  water,  as  in  the  wake  of  a  vessel  or 
on  the  crests  of  the  waves. 


197.  Temperature.  —  The  salts  dissolved  in 
ocean-water  lower  the  temperature  of  its  freez- 
ing-point. Ordinary  ocean-water  freezes  at  about 
27°  F.  In  places  where  the  water  is  salter,  the 
temperature  of  its  freezing-point  is  lower. 

Ice  formed  from  ocean-water  is  comparatively 
fresh,  nearly  all  the  salt  being  separated  as  the 
water  freezes  or  crystallizes.  The  salt,  thus  thrown 
out  from  the  frozen  water,  is  dissolved  by  the 
water  below,  lowers  the  temperature  of  its  freez- 
ing-point, and  thus  increases  its  density.  In  this 
manner  the  water  below  the  ice  may  have  a  tem- 
perature lower  than  that  at  which  the  surface- 
water  freezes,  and  yet  remain  liquid. 

In  the  polar  regions  the  water  below  the  sur- 
face is  at  a  temperature  lower  than  that  of  the 
freezing-point  of  the  surface-water.  This  cold 
water,  from  its  greater  density,  spreads  over  the 
floor  of  the  ocean  in  all  latitudes,  so  that,  except 
where  stirred  by  deep  currents,  the  entire  bottom 
of  the  ocean  is  covered  with  a  layer  of  dense, 
heavy  water,  the  temperature  of  which  is  nearly 
constant. 

The  temperature  of  this  water  is  about  35°  F.  Near 
the  poles  it  is  somewhat  lower :  about  29°,  or  a  little  higher 
than  its  maximum  density  of  the  surface-waters. 

The  upper  limit  of  this  line  of  invariable  temperature 
varies  with  the  latitude.  Near  the  equator,  where  the 
waters  are  heated  to  great  depths,  it  is  found  at  about 
10,000  feet  below  the  surface.  Toward  the  poles,  it  comes 
nearer  the  surface,  reaching  it  at  about  Lat.  60°,  from 
which  point  it  again  sinks,  being  found  at  Lat.  70°  at 
about  4500  feet  below  the  surface. 

In  the  tropics  the  temperature  of  the  surface-water 
is  about  80°  F. ;  in  the  polar  regions  it  is  near  the 
freezing-point.  The  ice  which  forms  in  the  polar 
regions  collects  in  vast  ice-fields  or  floes. 

198.  Shape  of  the  Bottom  of  the  Ocean.— The 
bed  of  the  ocean,  though  diversified  like  the  sur- 
face of  the  land,  contains  fewer  irregularities. 
Numerous  soundings  show  that  it  extends  for 
immense  distances  in  long  undulations  and  slopes. 
Its  plateaus  and  plains,  therefore,  are  of  great 
size,  compared  with  those  of  the  continents. 
Submerged  mountain-ranges  occur  both  in  the 
deep   ocean  and   along  the  shores.     The  latter 


74 


PHYSICAL    GEOGRAPHY. 


belong,  properly,  to  the  continental  systems  of 
elevations. 

199.  The  Oceanic  Areas. — The  ocean  is  one 
continuous  body  of  water,  but  for  purposes  of 
description  and  study  it  is  generally  divided  into 
five  smaller  bodies :  the  Pacific,  Atlantic,  Indian, 
Arctic,  and  Antarctic  Oceans.  The  last  two  are 
separated  from  the  preceding  by  the  polar  circles ; 
the  others  are  separated  mainly  by  the  continents. 
As  the  continents  do  not  extend  to  the  Antarctic 
Circle,  the  meridians  of  Cape  Horn,  Cape  of 
Good  Hope,  and  South  Cape  in  Tasmania,  are 
taken  as  the  ocean  boundaries  south  of  these 
points. 

The  following  table  gives  the  relative  size  of  the  oceanic 
areas : 

The  Pacific  occupies  about  \  the  entire  water-area. 
"    Atlantic     "  "       \  "  " 

"    Indian        "  "       }  "  " 

"    Antarctic  "  "      fr         H  " 

"    Arctic         "  "      ■& 

200.  Articulation  of  Land  and  Water. — The 
indentations  of  the  oceans,  or  the  lines  of  junc- 
tion between  the  water  and  the  land,  may  be 
arranged  under  four  heads: 

(1.)  Inland  Seas,  or  those  surrounded  by  a 
nearly  continuous  or  unbroken  land-border;  as 
the  Gulf  of  Mexico,  Hudson  Bay,  the  Baltic,  and 
the  Mediterranean,  in  the  Atlantic ;  the  Red  Sea 
and  the  Persian  Gulf,  in  the  Indian;  and  the 
Gulf  of  California,  in  the  Pacific. 

(2.)  Border  Seas,  or  those  isolated  from  the 
rest  of  the  ocean  by  peninsulas  and  island  chains ; 
as  the  Caribbean  Sea,  the  Gulf  of  St.  Lawrence, 
and  the  North  Sea,  in  the  Atlantic ;  and  Bering 
Sea,  the  Sea  of  Okhotsk,  the  Sea  of  Japan,  and 
the  North  and  South  China  Seas,  in  the  Pacific. 

(3.)  Gulfs  and  Bays,  or  broad  expansions  of 
the  water  extending  but  a  short  distance  into 
the  land ;  as  the  Gulf  of  Guinea  and  the  Bay  of 
Biscay,  in  the  Atlantic ;  and  the  Bay  of  Bengal 
and  the  Arabian  Sea,  in  the  Indian. 

(4.)  Fiords,  or  deep  inlets,  with  high,  rocky 
headlands,  extending  often  from  50  to  100  miles 
into  the  land.  One  of  the  best  instances  of  this 
form  of  indentation  is  off  the  Norway  coast.  Ac- 
cording to  Dana,  fiords  are  valleys  that  were  ex- 
cavated by  vast  ice-masses  called  glaciers,  but 
which  have  since  become  partially  submerged  by 
the  gradual  subsidence  of  the  land. 

Fiord  valleys  occur  on  the  Norway  coast,  on 
the  coasts  of  Greenland,  Labrador,  Nova  Scotia, 
and  Maine,  on  the  western  coast  of  Patagonia 


and  Chili,  and  on  the  western  coast  of  North 
America  north  of  the  Straits  of  Fuca.  On  parts 
of  the  coast  of  Greenland  the  glaciers  are  now 
cutting  out  their  partially  submerged  valleys, 
and  forming  what  will  probably  become  fiord 
valleys. 

The  Atlantic  Ocean  is  characterized  by  inland 
seas;  the  Pacific,  by  border  seas;  the  Indian,  by 
gulfs  and  bays;  the  Atlantic  and  the  Pacific,  by 
fiords. 

201.  Depth  of  the  Ocean. — The  mean  depth  of 
the  ocean  is  about  12,000  ft.,  or  nearly  2k  miles. 
Recent  soundings  give  the  greatest  depth  of  the 
Atlantic,  in  the  neighborhood  of  the  island  of 
St.  Thomas  of  the  West  Indies,  as  27,000  feet. 
The  greatest  depth  in  the  Pacific,  as  reported  by 
recent  careful  soundings,  occurs  east  of  Japan, 
and  is  27,930  ft.  These  give  a  depth  of  about 
5i  miles,  or  less  than  the  greatest  elevation  of  the 
land.  It  is  probable,  however,  that  some  portions 
of  the  ocean  are  much  deeper. 

The  greater  depressions  of  the  ocean  are  called 
deeps,  the  shallower  portions  are  called  rises. 

202.  The  Pacific  Ocean.— The  shape  of  the 
shore-line  of  the  Pacific  is  that  of  an  immense 
oval,  nearly  closed  at  the  north,  but  broad  and 
open  at  the  south. 

As  indicated  by  the  island  chains,  a  number  of  shallow 
places,  or  rises,  extend  in  the  direction  of  the  north-west 
trend  :  the  summits  of  those  on  the  north  form  the  Sand- 
wich Islands,  and  the  summits  of  those  on  the  south  form 
the  Polynesian  Island  chain. 

203.  The  Atlantic  Ocean. — The  shape  of  the 
shore-line  of  the  Atlantic  is  that  of  a  long, 
trough-like  valley,  with  nearly  parallel  sides. 
The  Atlantic  has  a  broad  connection  with  both 
the  polar  oceans,  and  forms  the  only  open  chan- 
nel for  the  intermingling  of  the  warm  and  cold 
waters. 

Shape  of  the  Bed. — Recent  soundings  in  the  Atlantic  show 
the  presence  of  a  submarine  plateau  extending  in  mid- 
ocean  parallel  to  the  coasts  of  the  continents  from  the  lati- 
tude of  the  southern  point  of  Africa  to  Iceland,  thus  di- 
viding the  basin  into  eastern  and  western  valleys.  The 
western  valley  is  the  deeper ;  the  average  depths  of  the  two 
being  respectively  18,000  and  13,000  feet.    A  remarkable 


Feet. 


Level  of  the  sea. 


Fig.  69.    The  Telegraphic  Plateau. 


plateau  extends  across  these  valleys,  from  Newfoundland 
to  Ireland.  Its  depth  ranges  from  10,000  to  nearly  13,000 
feet.  It  is  called  the  Telegraphic  Plateau,  and  bears  a 
number  of  telegraphic  cables.    The  eastern  and  western 


OCEANIC    MOVEMENTS, 


75 


valleys,  though  less  marked  in  this  region,  are  still  dis- 
tinguishable. 

The  true  bed  of  the  ocean  begins  at  a  considerable  dis- 
tance from  the  eastern  coast  of  North  America.  For  dis- 
tances of  from  75  to  100  miles,  the  depth  scarcely  exceeds 
600  feet ;  but  from  this  point  it  descends,  by  steep  terraces, 
to  profound  depths. 

The  British  Isles  are  connected  with  the  continent  of 
Europe  by  a  large  submerged  plateau,  which  underlies 
nearly  the  whole  North  Sea,  and  extends  for  considerable 
distances  off  the  western  and  southern  coasts.  The  depth 
of  this  part  of  the  ocean  is  nowhere  very  great. 

204.  The  Indian  Ocean. — The  shape  of  the 
shore-line  is,  in  general,  triangular.  This  ocean 
has  no  connection  with  the  Arctic,  but  is  entirely- 
open  on  the  south,  where  it  merges  into  the  great 
water-area  of  the  globe :  the  basins  of  the  Ant- 
arctic and  Pacific. 

Shape  of  the  Bed. — A  submarine  plateau  extends  to  the 
south  off  the  western  coast  of  Hindostan.  Its  summits 
form  the  Laccadive,  Maldive,  and  Chagos  Islands,  and  pos- 
sibly extends  in  the  same  direction  as  far  as  Kerguelen 
Island. 

205.  The  Antarctic  and  Arctic  Oceans.— The 
shore-line  of  the  Arctic  has  the  shape  of  an  ir- 
regular ring.  The  shore-line  of  the  Antarctic  is 
probably  of  the  same  shape. 

But  little  is  known  concerning  the  beds  of  these 
oceans.  From  the  very  limited  land-areas  south 
of  lat.  50°  S.,  the  bed  of  the  Antarctic  is  presum- 
ably deeper  than  that  of  the  Arctic,  except  toward 
the  south  pole,  where  it  is  probably  shallower. 

206.  Ooze  Deposits. — Foraminiferal  Land. — 
The  reef-forming  coral  polyps  are  not  the  only 
animalculse  the  accumulation  of  whose  bodies 
after  death  add  to  the  land-masses  of  the  earth. 
Deep-sea  soundings  show  that  over  extended  areas 


Fig,  70.    Foraminifera. 

the  floor  of  the  ocean  is  evenly  covered  with  a 
creamy  layer  of  mud  or  ooze,  which,  like  the 
deposits  of  the  coral  animalculse,  is  composed 
principally  of  carbonate  of  lime.  This  ooze  con- 
sists almost  entirely  of  microscopic  skeletons  of  a 


group  of  animalculse  known  as  the  Foraminifera, 
from  the  great  number  of  perforations  or  open- 
ings in  their  hard  parts.  These  animalculse  are 
so  small  that  1,000,000  are  equal  in  bulk  to  only 
one  cubic  inch.  They  appear  to  live  in  the  layers 
of  water  near  the  surface,  and  after  death  to 
fall  gradually  to  the  bottom  of  the  sea.  Sound- 
ings show  their  presence  over  very  extended 
areas. 

Many  of  the  very  deep  parts  of  the  ocean's  bed 
are  covered,  not  with  foraminiferal  deposits,  but 
with  a  layer  of  red  mud  composed  of  finely-di- 
vided clay.  Its  origin  is  probably  as  follows : 
In  very  deep  parts  of  the  ocean  before  the  fora- 
miniferal deposits  reach  the  bottom  their  limey 
matters  are  dissolved,  and  the  undissolved  parts 
form  the  deposits  of  fine  red  mud. 


CHAPTER   II. 

Oceanic  Movements. 

207.  The  Oceanic  Movements  can  be  arranged 
under  three  heads  :  waves,  tides,  and  currents. 

Waves  are  swinging  motions  of  the  water, 
caused  by  the  action  of  the  wind.  Their  height 
and  velocity  depend  on  the  force  of  the  wind,  and 
the  depth  of  the  basin  in  which  they  occur.  The 
stronger  the  wind,  and  the  deeper  the  ocean,  the 
higher  the  waves  and  the  greater  their  velocity. 


Fig.  71.    Ocean  Waves, 

Height  of  Waves. — Scoresby  measured  waves  in  the 
North  Atlantic  43  feet  above  the  level  of  the  trough. 
Waves  have  been  reported  in  the  South  Atlantic,  off  the 
Cape  of  Good  Hope,  between  50  and  60  feet  high.     Navi- 


76 


PHYSICAL    GEOGRAPHY. 


gators  have  occasionally  reported  higher  waves,  but  the 
accuracy  of  their  measurements  is,  perhaps,  to  he  doubted. 
In  the  open  sea,  with  a  moderate  wind,  the  height  of 
ordinary  waves  is  about  6  feet. 

The  distance  between  two  successive  crests  varies  from 
10  to  20  times  their  height.  Waves  4  feet  high  have 
their  successive  crests  40  feet  apart;  those  33  feet  high, 
about  500  feet  apart. 

208.  No  Progressive  Motion  of  Water  in 
Waves. — In  wave  motion,  the  water  seems  to  be 
moving  in  the  direction  in  which  the  wave  is  ad- 
vancing, but  this  is  only  apparent ;  light  objects, 
floating  on  the  water,  rise  and  fall,  but  do  not 
move  forward  with  the  wave.  In  shallow  water, 
however,  the  water  really  advances.  The  for- 
ward motion  of  the  wave  is  retarded,  so  that  the 
waves  following  reach  it,  thus  increasing  its 
height.  The  motion  at  the  bottom  is  lessened, 
and  the  top  curls  over  and  breaks,  producing 
what  are  called  breakers. 

On  gently  sloping  shores,  the  water  which  runs  down 
the  beach,  after  it  has  been  thrown  upon  it  by  the  breakers, 
forms,  at  a  little  distance  from  the  shore,  the  dreaded 
"undertow"  of  our  bathing-resorts. 

Force  of  the  Waves. — When  high,  and  moving 
in  the  direction  of  the  wind,  the  waves  dash 
against  any  obstacle,  such  as  a  line  of  coast,  with 
great  force,  and  may  thus  cut  it  away  and  change 
the  coast-line.  This  action  occurs  only  on  ex- 
posed, shelving  coasts.  The  wave-motion  is,  in 
general,  very  feeble  at  40  feet  below  the  surface. 
The  eroding  action  of  the  ocean  waves  is,  there- 
fore, far  inferior  to  that  of  the  continental  waters. 

209.  Tides  are  the  periodical  risings  and  fall- 
ings of  the  water,  caused  by  the  attraction  of  the 
sun  and  moon.  The  alternate  risings  and  fallings 
succeed  each  other  with  great  regularity,  about 
every  six  hours.  Unlike  waves,  in  which  the 
motion  is  confined  practically  to  the  surface 
waters  only,  tides  affect  the  waters  of  the  ocean 
from  top  to  bottom. 

The  rising  of  the  water  is  called  flood  tide ;  the 
falling,  ebb  tide.  When  the  waters  reach  their 
highest  and  lowest  points,  they  remain  stationary 
for  a  few  minutes.  These  points  are  called,  re- 
spectively, high  and  low  water.  Corresponding 
high  or  low  water,  at  any  place,  occurs  fifty-two 
minutes  later  each  successive  day. 

210.  Theory  of  the  Tides.— If  the  earth  were 
uniformly  covered  with  a  layer  of  water,  the  pas- 
sage of  the  moon  over  any  place,  as  at  a,  Fig.  72, 
would  cause  the  water  to  lose  its  globular  form, 
become  bulged  at  a,  and  b,  and  flattened  at  e, 
and  d.     In  other  words,  the  water  would  become 


deeper  at  a,  and  b,  at  the  parts  of  the  earth  near- 
est and  farthest  from  the  moon,  and  shallower  in 


! 


o 


Fig.  72,    Lunar  Tide. 

all  places  90°  or  at  right  angles  to  these  points, 
such,  for  example,  as  at  c,  and  d. 

This  deepening  and  shallowing  of  the  water  is 
caused  by  the  attraction  of  the  moon.  As  the 
moon  passes  over  a,  the  water  is  drawn  toward 
the  moon,  thus  deepening  the  water  directly  under 
the  moon,  and  shallowing  it  at  c,  and  d. 

The  cause  of  the  deepening  of  the  water  at  6, 
on  the  side  farthest  from  the  moon,  is  as  follows : 
the  solid  earth  being,  as  a  whole,  nearer  the  moon 
than  the  water  at  b,  but  farther  from  it  than  that 
at  a,  must  take  a  position  which  will  be  nearly 
midway  between  a,  and  b,  leaving  a  protuberance 
at  b,  nearly  equal  to  that  at  a. 

The  protuberances  a,  and  b,  mark  the  position 
of  high  tides.  At  all  points  of  the  earth  90°  from 
the  protuberances,  as  at  e,  and  d,  the  depression  is 
greatest.     These  mark  the  position  of  low  tides. 

High  tides,  then,  occur  at  those  points  of  the 
earth's  surface  which  are  cut  by  a  straight  line, 
which  passes  through  the  centre  of  the  earth  and 
that  of  the  attracting  body,  as  the  sun  or  moon. 
Low  tides  are  found  at  right  angles  to  these 
points. 

Had  the  earth  no  rotation,  the  tidal  waves,  so 
formed,  would  slowly  follow  the  moon  in  its  mo- 
tion around  the  earth.  But,  by  the  rotation  of 
the  earth,  different  parts  of  its  surface  are  rapidly 
brought  under  the  moon,  and  the  tidal  waves, 
consequently,  move  rapidly  from  one  part  of  the 
ocean  to  another. 

Had  the  moon  no  motion  around  the  earth,  there  would 
be  two  high  tides  and  two  low  tides  every  24  hours. 
While,  however,  the  earth  is  making  one  complete  rota- 
tion, the  moon,  in  its  motion  around  the  earth,  has 
changed  its  position,  and  the  earth  rotates  for  52  minutes 
longer  before  the  same  point  again  comes  directly  under 
the  moon. 

Since  the  uniformity  of  the  water  surface  is 
broken  by  the  elevations  of  the  land,  the  progress 
of  the  tidal  wave  is  greatly  affected  by  the  size, 
shape,  and  depth  of  the  oceanic  basin,  and  the 


OCEANIC    MOVEMENTS. 


77 


position  of  the  continents.  Owing  to  the  obstruc- 
tions offered  by  the  continents,  and  by  inequalities 
in  the  bed  of  the  ocean,  a  very  considerable  re- 
tardation of  the  tidal  wave  is  effected,  so  that  a 
high  tide  may  not  occur  at  a  place  until  long 
after  the  moon  has  passed  over  it. 

Solar  Tides. — The  sun  also  produces  a  system 
of  tidal  waves,  but  owing  to  its  greater  distance 
from  the  earth,  the  tides  thus  produced  are  much 
smaller  than  those  of  the  moon,  upon  which,  there- 
fore, they  exert  but  a  modifying  influence.  The 
tide-producing  power  of  the  moon  is  greater  than 
that  of  the  sun,  in  about  the  proportion  of  800 
to  355.  That  is,  the  tide  produced  by  the  moon 
is  about  24  times  greater  than  that  produced  by 
the  sun. 

The  tidal  wave  moves,  in  general,  from  east  to  west,  or  in 
the  opposite  direction  to  the  rotation  of  the  earth.  The  motion 
of  so  large  a  mass  of  water  thus  opposed  to  the  earth's  ro- 
tation, must  gradually  diminish  the  axial  velocity,  and, 
eventually,  entirely  ■stop  the  rotation  of  the  earth ;  in  this 
way  an  increase  in  the  length  of  day  and  night  should  be 
produced,  but  so  far,  however,  no  increase  has  been  de- 
tected, although  astronomical  observations  extend  back- 
ward for  loug  periods.  The  increased  axial  velocity,  pro- 
duced by  the  contraction  of  the  globe,  probably  balances 
the  retarding  influence  of  the  tides. 

In  the  deep  ocean,  and  near  the  mouths  of  rivers,  the 
duration  of  the  flood  and  ebb  are  about  equal ;  but  in  most 
rivers,  at  some  distance  from  the  mouth,  the  ebb  is  longer 
than  the  flood.  The  cause  is  to  be  found  in  the  fact  that 
the  outflowing  river  current  meets  and  temporarily  neu- 
tralizes the  inflowing  flood  tide,  thus  diminishing  its  dura- 
tion, and  afterward,  adding  its  motion  to  the  ebb,  makes 
the  difference  between  the  two  still  greater. 

The  tidal  wave  often  ascends  a  stream  to  a  much  greater 
elevation  above  the  level  of  its  mouth  than  the  height  of 
the  tide  at  the  river's  mouth.  In  large  rivers,  like  the 
Amazon,  the  tidal  wave  advances  up  the  river  as  much  as 
100  feet  above  the  sea-level. 


Some  of  the  proofs  of  the  connection  between  the  tides 
and  the  attraction  of  the  moon  and  sun  are  as  follows : 

(1.)  The  interval  between  corresponding  high  tides  at 
any  place  is  the  same  as  the  interval  between  two  succes- 
sive passages  of  the  moon  over  that  place:  24  hours,  52 
minutes. 

(2.)  The  tides  are  higher  when  the  moon  is  nearer  the 
earth. 

(3.)  The  tides  are  higher  when  the  sun  and  moon  are 
simultaneously  acting  to  cause  high  tides  in  the  same 
places 

Quarter. 


# 


» : 


'!:■ 
ill 


Neap  Tides,  • 

flood  and  ebb  ' 
moderate.      \ 


SUN 


."x 


Quarter.     ^ 
Fig,  73.    Cause  of  the  Phases  of  the  Moon, 

Phases  of  the  Moon. — An  inspection  of  Fig.  73  will 
show,  that  during  new  and  full  moon,  the  earth,  moon, 
and  sun  are  all  in  the  same  straight  line,  but,  that  during 
the  first  and  last  quarters,  they  are  at  right  angles.  The 
portions  of  the  earth  and  moon  turned  toward  the  sun  are 
illumined,  the  shaded  portions  are  in  the  darkness.  To 
an  observer  on  the  earth,  the  moon,  at  a,  appears  new, 
since  the  dark  part  is  turned  toward  him ;  at  b,  however, 
it  must  appear  full,  since  the  illumined  portions  are  toward 
him.  At  c,  and  d,  the  positions  of  the  quarters,  only  one- 
half  of  the  illumined  half,  or  one  quarter,  is  seen. 


Spring  Tides, 

flood  and  ebb 

excessive. 


Tig.  74.    Position  of  the  Earth,  Moon,  and  Sun  during  Spring  and  Neap  Tides. 


211.  Spring  and  Neap  Tides. — When  the  sun 
and  moon  act  simultaneously,  on  the  same  hemi- 
sphere of  the  earth,  as  shown  in  Fig.  74,  the  tidal 
wave  is  higher  than  usual.  The  flood  tides  are 
then  highest,  and  the  ebb  tides  lowest.  These 
are  called  spring  tides.  They  occur  twice  during 
10 


every  revolution  of  the  moon — once  at  full,  and 
once  at  new  moon.  The  highest  spring  tides  oc- 
cur a  short  time  before  the  March  and  the  Sep- 
tember equinoxes,  when  the  sun  is  over  the  equa- 
tor, and  is  nearest  the  earth. 

When,  however,  the  sun  and  moon  are  90° 


78 


PHYSICAL    GEOGRAPHY. 


apart,  or  in  quadrature,  each  produces  a  tide  on 
the  portion  of  the  earth  directly  under  it,  dimin- 
ishing somewhat  that  produced  by  the  other  body. 
High  tide,  then,  occurs  under  the  moon,  while  the 
high  tide  caused  by  the  sun,  becomes,  by  compari- 
son, a  low  tide.  Such  tides  are  called  neap  tides. 
During  their  prevalence,  the  flood  is  not  very 
high,  nor  the  ebb  very  low.  They  occur  twice 
during  each  revolution  of  the  moon,  but  are  low- 
est about  the  time  of  the  June  and  December 
solstices. 

The  average  relative  height  of  the  spring  tide  to  that 
of  the  neap  tide  is  about  as  7  to  4. 

212.  Birthplace  of  the  Tidal  Wave.— Although 
a  tidal  wave  is  formed  in  all  parts  of  the  ocean 
where  the  moon  is  overhead,  yet  the  "  Cradle  of 
the  Tides  "  may  properly  be  located  in  the  great 
southern  area  of  the  Pacific  Ocean.  Here  the 
combined  attraction  of  the  sun  and  moon  origin- 


ate a  wave,  which  would  travel  around  the  earth 
due  east  and  west,  with  its  crests  north  and  south ; 
but,  meeting  the  channels  of  the  oceans,  it  is 
forced  up  them  toward  the  north.  Its  progress  is 
accelerated  in  the  deep  basins,  and  retarded  in  the 
shallow  ones.  On  striking  the  coasts  of  the  con- 
tinents, deflected  or  secondary  waves  move  off  in 
different  directions,  thus  producing  great  com- 
plexity in  the  form  of  the  parent  wave. 

213.  Co-Tidal  Lines.— The  progress  of  the  tidal 
wave,  in  each  of  the  oceans,  is  best  understood  by 
tracing  on  a  map,  lines  connecting  all  places 
which  receive  the  tidal  wave  at  the  same  time. 
These  are  called  co-tidal  lines.  The  distance  be- 
tween two  consecutive  lines  represents  the  time,  in 
hours,  required  for  the  progress  of  the  tidal  wave. 
In  parts  of  the  ocean  where  the  wave  travels  rap- 
idly the  co-tidal  lines  are  far  apart ;  when  its  prog- 
ress is  retarded,  they  are  crowded  together. 


Fig.  75.    Co- Tidal  Chart, 


Since  it  is  only  possible  to  take  the  height  of  the  tide 
on  the  coasts  of  islands  and  of  the  continents,  the  tracks 
of  the  co-tidal  lines  must  be  to  a  considerable  extent  con- 
jectural. 

214.  The  Pacific  Ocean. — Twice  every  day  a 
tidal  wave  starts  in  the  south-eastern  part  of  the 
Pacific  Ocean,  west  of  South  America,  somewhere 
between  the  two  heavy  lines  marked  xn  on  the 


chart.  It  advances  rapidly  toward  the  north- 
west in  the  deep  valley  of  this  ocean,  reaching 
Kamtchatka  in  about  6  hours.  Toward  the  west 
its  progress  is  retarded  by  the  shallower  water, 
and  by  the  numerous  islands,  so  that  it  only 
reaches  New  Zealand  in  about  6  hours  and  enters 
the  Indian  Ocean  in  about  12  hours. 

215.  The  Indian  Ocean. — The  12-hour-old  tidal 


OCEAN    CURRENTS. 


79 


wave  from  the  Pacific,  meets  and  moves  along 
with  a  wave  started  in  this  ocean  by  the  moon, 
and  advances  in  the  direction  indicated  by  the 
co-tidal  lines  entering  the  Atlantic  Ocean  about 
12  hours  afterward. 

216.  The  Atlantic  Ocean. — The  tidal  wave  from 
the  Indian  joins  two  other  waves,  one  formed  by 
the  moon  in  this  ocean,  and  the  other  a  deflected 
wave  that  has  backed  into  the  Atlantic  from  the 
Pacific.  The  tidal  wave  thus  formed  advances 
rapidly  up  the  deep  valley  of  the  Atlantic,  reach- 
ing Newfoundland  12  hours  afterward,  or  48  hours 
after  it  started  in  the  Pacific.  It  then  advances 
rather  less  rapidly  toward  the  north-east,  reach- 
ing the  Loffoden  Islands  12  hours  afterward,  or 
60  hours  after  leaving  its  starting-place  in  the 
Pacific. 

217.  Tides  in  Inland  Seas  and  Lakes  are  very 
small  and,  consequently,  difficult  to  detect.  In 
the  Mediterranean  Sea  the  tides  on  the  coasts 
average  about  18  inches.  The  tide  in  Lake 
Michigan  is  about  If  inches. 

218.  Height  of  Tidal  Wave. — Ocean  tides  are 
lowest  in  mid-ocean,  where  they  range  from  two 
to  three  feet.  Off  the  coasts  of  the  continents, 
especially  when  forced  up  narrow,  shelving  bays, 
deep  gulfs,  or  broad  river  mouths,  they  attain 
great  heights.  The  cause  of  these  unusual  heights 
is  evident.  When  the  progress  of  the  tidal  wave 
is  retarded,  either  by  the  contraction  of  the  chan- 
nel or  by  other  causes,  the  following  part  of  the 
wave  overtakes  the  advanced  part,  and  thus,  what 
the  ivave  loses  in  speed  it  gains  in  height,  from  the 
heaping  up  of  the  advancing  waters.  Where  the 
co-tidal  lines,  therefore,  are  crowded  together  on  the 
chart,  high  tides  are  likely  to  occur ;  for  example, 
the  Arabian  Sea  and  Bay  of  Bengal,  the  North 
and  South  China  Seas,  the  eastern  coasts  of  Pata- 
gonia, the  Bay  of  Fundy,  the  English  Channel, 
and  the  Irish  Sea,  have  very  high  tides. 

Near  the  heads  of  the  Persian  Gulf  and  China 
Seas,  the  tides  sometimes  rise  about  36  -feet.  At 
the  mouth  of  the  Severn,  the  spring  tides  rise 
from  45  to  48  feet ;  on  the  southern  coast  of  the 
English  Channel,  50  feet ;  and  in  the  Bay  of 
Fundy,  near  the  head,  the  spring  tides,  aided  by 
favoring  winds,  sometimes  reach  70  feet,  and,  oc- 
casionally, even  100  feet. 

A  strong  wind,  blowing  in  the  direction  in  which  the 
tidal  wave  is  advancing,  causes  an  increase  in  the  height 
of  the  tide. 

A  low  barometer  is  attended  by  a  higher  tide  than 
usual ;  a  high  barometer,  by  a  lower  tide. 


219.  Other  Tidal  Phenomena. 

The  Bore  or  Eager. — On  entering  the  estuary  of  a 
river,  the  volume  of  whose  discharge  is  considerable,  the 
onward  progress  of  the  tidal  wave  is  checked ;  but,  piling 
up  its  waters,  the  incoming  tide  at  last  overcomes  the  re- 
sistance of  the  stream,  and  advances  rapidly,  in  several 
huge  waves.  The  tides'  of  the  Hoogly,  the  Elbe,  the 
Weser,  and  the  Amazon,  are  examples.  In  the  latter 
river,  the  wave  is  said  to  rise  from  30  to  50  feet. 

Races  and  Whirlpools. — When  considerable  differ- 
ences of  level  are  caused  by  the  tides,  in  parts  of  the  ocean 
separated  by  narrow  channels,  the  waters,  in  their  effort 
to  regain  their  equilibrium,  move  with  great  velocity,  pro- 
ducing what  are  called  races.  At  times,  several  races  meet 
each  other  obliquely,  thus  producing  whirlpools.  Near  the 
Channel  Islands,  and  off  the  northern  coasts  of  Scotland, 
races  are  numerous.  The  Maelstrom,  off  the  coasts  of  Nor- 
way, is  an  instance  of  a  whirlpool,  though  the  motion  of 
the  waters  is  not  exactly  a  whirling  one.  The  main  phe- 
nomenon is  a  rapid  motion  of  the  waters,  alternately  back- 
ward and  forward,  caused  by  the  conflict  of  tidal  currents 
off  the  Loffoden  Islands. 


K>J#<C 


CHAPTER   III. 
Ocean  Currents. 

220.  Constant  Ocean  Currents. — Besides  tidal 
currents,  the  waters  of  the  ocean  are  disturbed 
to  great  depths,  by  currents,  moving  with  consid- 
erable regularity  to  and  from  the  equatorial  and 
polar  regions,  and  thus  producing  a  constant  in- 
terchange of  their  waters.  These  movements  are 
called  constant  currents,  and,  unlike  waves,  con- 
sist in  a  real,  onward  movement  of  the  water. 

Constant  currents  resemble  rivers,  but  are  im- 
mensely broader  and  deeper.  As  a  rule,  their 
temperature  differs  considerably  from  that  of  the 
waters  through  which  they  flow.  They  are  not 
confined  to  the  surface,  but  exist  as  well  at  great 
depths,  when  they  are  called  under  or  counter  cur- 
rents, and  flow  in  a  direction  opposite  to  that  of  the 
surface  currents. 

221.  The  Principal  Cause  of  Constant  Ocean 
Currents  is  the  difference  of  density  of  the  water 
produced  by  the  differences  of  temperature  be- 
tween the  equatorial  and  the  polar  regions. 

As  the  waters  of  the  polar  regions  lose  their 
heat  they  become  denser,  and,  sinking  to  the  bot- 
tom, form  a  mountain-like  accumulation  of  dense, 
cold  water,  which,  as  rapidly  as  formed,  spreads 
over  the  floor  of  the  ocean  underneath  the  lighter 
waters.  The  consequent  lowering  of  the  level  of 
the  polar  waters  causes  an  influx  of  the  surface 
waters  from  the  equatorial  regions.  In  this  man- 
ner a  constant  interchange  is  effected  between  the 


80 


PHYSICAL    GEOGRAPHY. 


equatorial  and  polar  regions,  which,  for  the  greater 
part,  takes  place  along  the  bottom  from  the  poles 
to  the  equator,  and  along  the  surface  from  the 
equator  to  the  poles.  Since,  however,  the  pole  is 
a  mere  point,  this  interchange  occurs  mainly  be- 
tween the  equator  and  the  polar  circles. 


Fig.  76,    Currents  caused  by  Difference  of  Temperature. 

Thus  in  Fig.  76,  the  mountain-like  accumula- 
tion is  shown  as  having  its  crest  at  about  the  lati- 
tude of  the  polar  circle.  The  arrows  show  the 
direction  of  the  currents.  At  the  equatorial  re- 
gions, the  surface  water  is  warmer  and  lighter, 
and  at  the  polar  regions,  probably,  colder  and 
lighter. 

As  a  rule,  the  warm  currents  are  on  the  surface,  and  the 
cold  currents,  from  their  greater  density,  are  underneath 
them.  In  shallow  oceans,  however,  the  cold  currents  come 
to  the  surface,  thus  displacing  the  warm  currents  and  de- 
flecting them  to  deeper  parts  of  the  ocean. 

Had  the  earth  no  rotation  on  its  axis,  this  in- 
terchange would  be  due  north  and  south,  or  would 
take  place  directly  between  the  equatorial  and 
polar  regions.  On  account  of  the  earth's  rota- 
tion, however,  and  a  variety  of  other  causes, 
these  north-and-south  directions  are  consider- 
ably changed.  The  principal  of  these  deflecting 
causes  are — 

(1.)  The  earth's  rotation ; 

(2.)  The  position  of  the  land  masses 

(3.)  The  winds ; 

(4.)  Differences  of  density  caused  by  evapora- 
tion ; 

(5.)  Differences  of  level  caused  by  evapora- 
tion. 

The  changes  in  direction  caused  hy  the  earth's  rotation 
and  the  position  of  the  land  masses  are  as  follows :  as  the 
waters  are  in  constant  motion,  the  polar  waters  reach  the 
equatorial  regions  with  an  eastward  motion  less  than  that 
of  the  earth.  In  the  equatorial  regions,  therefore,  the 
waters  are  unahle  to  acquire  the  earth's  motion  toward  the 
east,  and  are  left  behind ;  that  is,  the  earth,  slipping  from 
under  them,  causes  them  to  cross  the  ocean  at  a,  a',  Fig. 
77,  from  east  to  west,  although  they  are  in  reality  moving 
with  the  earth  toward  the  east. 

Reaching  the  western  borders  of  the  oceans,  near  b,  b', 
the  continents  prevent  their  going  farther  west,  and  de- 
flect them  into  northern  and  southern  branches,  and  they 
begin  to  move  toward  the  poles. 

From  c,  to  d,  and  from  c',  to  d',  the  poleward-moving 
waters  are  deflected  toward  the  east  in  both  hemispheres. 


The  waters  on  reaching  c,  from  a,  and  6,  still  retain  the 
eastward  motion  they  acquired  while  moving  with  the 

d 


Fig.  77.    Deflections  of  Ocean  Currents. 


earth.  This  motion  is  greater  than  that  of  the  earth  be- 
tween c,  and  d.  Between  these  points,  therefore,  the  water 
is  acted  on  by  two  forces,  one  tending  to  carry  it  toward 
the  poles,  and  the  other  tending  to  carry  it  eastward. 
The  resultant  of  these  forces  carries  the  water  from  c,  to 
d,  and  from  c',  to  d',  or  toward  the  north-east  in  the  North- 
ern, and  toward  the  south-east  in  the  Southern  Hemisphere. 

Between  d,  and  e,  and  d',  and  e',  the  waters  still  retain 
this  excess  of  eastward  motion,  and,  therefore,  move  in 
the  directions  shown. 

Between  e,  and  a,  and  e',  and  a',  the  waters  in  both  hemi- 
spheres are  deflected  toward  the  west  because  they  are 
unable  to  acquire  the  earth's  motion  toward  the  east. 
Another,  and  perhaps  the  main,  cause  of  this  westward 
deflection  is  the  depression  caused  by  the  westward  move- 
ment of  the  equatorial  waters  at  a,  and  a'. 

The  action  of  the  winds  is  to  tend  to  move  the  surface 
waters  in  the  direction  in  which  they  are  blowing.  This 
action  is  by  some  authorities  regarded  as  the  principal 
cause  of  constant  currents. 

The  difference  in  the  density  of  the  water,  caused  by 
evaporation,  leaving  the  water  Salter  and  denser  in  some 
parts,  and  fresher  and  lighter  in  others,  probably  acts  to 
some  extent  as  a  deflecting  cause.  For  example,  the  water 
evaporated  near  the  equator,  and  precipitated,  for  the 
greater  part,  in  regions  near  the  borders  of  the  tropics, 
renders  the  regions  Salter  and  denser  from  which  it  was 
evaporated,  and  fresher  and  less  dense  where  it  is  precipi- 
tated. , 

The  difference  in  level  caused  by  the  greater  evapora- 
tion in  the  equatorial  regions  north  of  the  equator  than 
in  corresponding  latitudes  in  the  Southern  Hemisphere 
has  been  ascribed  as  one  of  the  causes  of  the  flow  of  Ant- 
arctic waters  toward  the  equator. 

222.  General  Features  of  Constant  Currents. — 
The  following  motions  of  the  surface  currents  are 
common  to  all  the  three  central  oceans : 

(1.)  A  movement  of  the  equatorial  waters,  a,a, 
from  east  to  west ; 

(2.)  Their  deflection  into  northern  and  south- 
ern branches  (b  and  c),  on  reaching  the  western 
borders  of  the  ocean ; 

(3.)  A  movement  of  the  waters  beyond  the 
equator  from  west  to  east  (d,  e)  ; 


Page  ft. 


82 


PHYSICAL    GEOGRAPHY. 


(4.)  A  separation  of  these  latter  currents  into 
two  branches  (J,  g  and  h,  i),  one  continuing  toward 


a— Equator. 


Fig,  78.    Chart  of  Constant  Currents. 

the  poles,  and  the  other  toward  the  equator,  where 
they  join  with  the  equatorial  currents,  thus  com- 
pleting a  circuit  in  the  shape  of  a  vast  ellipse ; 

(5.)  A  flow  of  the  Arctic  waters  along  the 
western  border  of  the  ocean  (j),  and  of  the  Ant- 
arctic along  the  eastern  (k). 

Since  the  Indian  Ocean  is  completely  closed  on  the 
north,  only  part  of  the  above  movements  are  observed. 
In  the  Pacific,  an  equatorial  counter-current  crosses  the 
ocean  from  west  to  east. 

223.  Currents  of  the  Atlantic. — The  equatorial 
current  crosses  the  ocean,  from  east  to  west,  in 
two  branches :  a  south  equatorial  current,  which 
comes  from  the  Antarctic,  and  a  north  equatorial 
current,  which  comes  mainly  from  regions  north 
of  the  equator. 

The  north  equatorial  current  flows  along  the 
north-east  coast  of  South  America,  and,  for  the 
greater  part,  enters  the  Caribbean  Sea  and  Gulf 
of  Mexico,  and  emerges  between  Florida  and 
Cuba  as  the  Gulf  Stream. 

The  Gulf  Stream  flows  along  the  eastern  coast 
of  North  America,  with  a  velocity  of  from  four  to 
five  miles  per  hour,  and  in  mid-ocean,  between 
Newfoundland  and  Spain,  divides,  one  branch 
flowing  toward  Norway,  Spitzbergen,  and  Nova 
Zembla,  the  other  flowing  southward,  down  the 
coasts  of  Africa,  where  it  forms  the  main  feeder 
of  the  north  equatorial  current. 

The  south  equatorial  current,  after  crossing  the 
ocean,  flows  south  along  the  Brazilian  coast,  and 
divides  near  Rio  Janeiro,  the  main  part  flowing 
eastward  and  mingling  with  the  Antarctic  cur- 
rent, and  the  remainder  continuing  down  the  east- 


ern coast  of  South  America.  Cold  currents  from 
the  Arctic  flow  down  the  coasts  of  Greenland  and 
Labrador.  A  broad  polar  current  sweeps  from 
the  Antarctic  Ocean,  and  forms  the  main  feeder 
of  the  south  equatorial  current,  but  passes  in 
greater  part  eastward,  south  of  Africa. 

A  small  elliptical  current  flows  near  the  equator, 
between  the  north  and  south  equatorial  currents. 

224.  Currents  of  the  Pacific. — North  and  south 
equatorial  currents  flow  from. east  to  west,  and 
between  them  a  smaller,  less  powerful  equatorial 
counter-current,  from  west  to  east.  The  south 
equatorial  current,  fed  by  the  broad  Antarctic 
current,  is  the  larger  of  the  two. 

The  north  equatorial  current,  on  reaching  the 
Philippine  Islands,  divides  into  northern  and 
southern  branches ;  a  portion  of  its  southern 
branch  returns  with  the  equatorial  counter-cur- 
rent, while  the  northern  branch,  the  main  por- 
tion, flows  north-east  along  the  Asiatic  coast  as 
the  Kuro  Sivo,  the  counterpart  of  the  Gulf 
Stream.  At  about  Lat.  50°,  this  flows  east- 
wardly  as  a  North  Pacific  current,  and  off  the 
shores  of  North  America  it  returns,  in  an  ellip- 
tical path,  southerly  to  the  north  equatorial  cur- 
rent, forming  its  main  feeder.  A  small  current 
flows  through  the  eastern  side  of  Bering  Strait, 
into  the  Arctic  Ocean. 

The  south  equatorial  current  of  the  Pacific  is 
broken  into  numerous  branches  during  its  passage 
through  the  islands  in  mid-ocean.  Reaching  the 
Australian  continent  and  the  neighboring  archi- 
pelagoes, it  sends  small  streams  toward  the  north, 
but  the  main  portion  flows  south,  along  the  Aus- 
tralian coast,  when,  flowing  eastward,  it  merges 
with  the  cold  Antarctic  current. 

The  Antarctic  current  moves  as  a  broad  belt 
of  water  toward  the  north-east,  when,  flowing  up 
the  western  coast  of  South  America,  it  turns  to 
the  west,  and  forms  the  main  feeder  of  the  south 
equatorial  current.  A  part  of  the  Antarctic  cur- 
rent flows  eastward,  south  of  South  America,  and 
enters  the  Atlantic  as  the  Cape  Horn  current. 

A  small  cold  current  from  the  Arctic  flows 
through  Bering  Strait,  down  the  Asiatic  coast. 

225.  Currents  of  the  Indian  Ocean. — Only  a 
south  equatorial  current  exists,  which  flows  down 
the  eastern  and  western  coasts  of  Madagascar,  and 
down  the  African  coast  to  Cape  Agulhas,  when, 
turning  eastward,  it  merges  with  the  Antarctic 
current,  and  flows  up  the  western  coast  of  Aus- 
tralia, where  it  joins  the  equatorial  current. 


The  north  equatorial  current  in  this  ocean  is  indistinct — 

(1.)  Because  the  ocean  has  no  outlet  to  the  north ; 

(2.)  Powerful  seasonal  winds,  called  the  monsoons,  move 
the  waters  alternately  in  different  directions,  as  huge  drift 
currents. 

Sargasso  Seas. — Near  the  centre  of  the  ellip- 
tical movement  in  each  of  the  central  oceans, 
masses  of  seaweed  have  collected  where  the  water 
is  least  disturbed.     These  are  called  sargasso  seas. 


226.  Utility  of  Currents : 

(1.)  They  moderate  the  extremes  of  climate  by 
carrying  the  warm  equatorial  waters  to  the  poles, 
and  the  cold  polar  waters  to  the  equator ; 

(2.)  They  increase  materially  the  speed  of  ves- 
sels sailing  in  certain  directions ; 

(3.)  They  transport  large  quantities  of  timber 
to  high  northern  latitudes. 


SYLLABUS. 


Ocean  water  contains  ahout  three  and  one-third  pounds 
of  various  saline  ingredients,  in  e^ry  one  hundred.  Chlo- 
ride of  sodium ;  sulphates  and  carbonates  of  lime,  mag- 
nesia, and  potassa;  and  various  chlorides,  bromides,  and 
iodides,  are  the  principal  saline  ingredients. 

The  salt  of  the  ocean  is  derived  either  from  the 
washings  of  the  land,  or  is  dissolved  out  from  the  por- 
tions of  the  crust  which  are  continually  covered  by  its 
waters. 

The  ocean  is  Salter  in  those  parts  where  the  evaporation 
exceeds  the  rainfall.  Seas  like  the  Mediterranean,  which 
are  connected  with  the  ocean  by  narrow  channels,  and  in 
which  the  evaporation  is  greater  than  the  rainfall,  are 
Salter  than  the  ocean.  Others,  like  the  Baltic,  in  which 
the  rainfall  exceeds  the  evaporation,  are  fresher  than  the 
ocean. 

Most  of  the  bed  of  the  ocean  is  covered  with  a  layer  of 
dense  water,  at  about  the  temperature  of  its  maximum 
density. 

The  Pacific  and  Atlantic  Oceans  occupy  about  three- 
fourths  of  the  entire  water-area  of  the  earth. 

South  of  the  southern  extremities  of  South  America, 
Africa,  and  Australia,  the  meridians  of  Cape  Horn,  Cape 
Agulhas,  and  South  Cape  in  Tasmania,  are  assumed  as 
the  eastern  boundaries  of  the  Pacific,  Atlantic,  and  Indian 
Oceans. 

The  articulation  of  land  and  water  assumes  four  distinct 
forms :  Inland  Seas,  Border  Seas,  Gidfs  and  Bays,  and  Fiords. 
Inland  Seas  characterize  the  Atlantic  ;  Border  Seas,  the  Pa- 
cific; Gulfs  and  Bays,  the  Indian  Ocean;  and  Fiords,  the 
Atlantic  and  Pacific. 

The  telegraphic  plateau  lies  between  Ireland  and  New- 
foundland.    Its  average  depth  is  about  two  miles. 

The  bottom  of  the  ocean  is  not  as  much  diversified  as 
the  surface  of  the  land.  Its  plateaus  and  plains  are  be- 
lieved to  be  much  broader  than  are  those  of  the  land.  The 
profound  valleys  of  the  ocean  are  called  deeps,  its  shallow 
parts,  rises. 

The  greatest  depth  of  the  ocean  that  has  as  yet  been 
accurately  sounded  is  about  5J  miles.  It  is  probably  deeper 
than  this  in  some  places. 

Over  extended  areas,  the  floor  of  the  ocean  is  uniformly 
covered  with  a  deposit  of  fine  calcareous  mud  or  ooze, 
formed  of  the  hard  parts  of  the  bodies  of  minute  animal- 
culse. 

The  movements  of  the  oceanic  waters  may  be  arranged 
under  the  three  heads :  waves,  tides,  and  currents. 


The  height  and  velocity  of  a  wave  depend  upon  the 
force  of  the  wind  and  the  depth  of  the  oceanic  basin. 

In  ordinary  wave  motion,  the  water  rises  and  falls,  but 
does  not  move  forward. 

Tides  are  the  periodical  risings  and  fallings  of  the  water, 
caused  by  the  attraction  of  the  sun  and  moon. 

The  rising  of  the  water  is  called  flood  tide ;  the  falling, 
ebb  tide. 

If  the  earth  were  uniformly  covered  with  a  layer 
of  water,  two  high  tides  would  occur  simultaneously; 
one  on  the  side  of  the  earth  directly  under  the  sun 
or  moon,  the  other  on  the  side  farthest  from  the  sun 
or  moon. 

The  tidal  wave  crosses  the  ocean  from  east  to  west,  fol- 
lowing the  moon  in  the  opposite  direction  to  that  in  which 
the  earth  passes  under  it  while  rotating.  Its  progress  is 
considerably  retarded  by  the  projections  of  the  continents, 
and  the  shape  of  the  oceanic  beds.  Had  the  moon  no  real 
motion  around  the  earth,  there  would  be  two  high  and 
two  low  tides  every  twenty-four  hours,  or  the  high  and 
low  tides  would  be  exactly  six  hours  apart. 

Spring  Tides  are  caused  by  the  combined  attractions  of 
the  sun  and  moon  on  the  same  portions  of  the  earth.  Neap 
tides  by  their  opposite  attractions. 

The  parent  tidal  wave  is  considered  as  originating  in 
the  great  water-area  of  the  Pacific  on  the  south. 

Co-tidal  lines  are  lines  connecting  places  which  have 
high  tides  at  the  same  time. 

When  the  progress  of  the  tidal  wave  is  retarded  by  the 
c!ielving  coast  of  a  continent,  what  the  tide  loses  in  speed, 
it  gains  in  height.  The  highest  tides,  therefore,  occur 
where  the  co-tidal  lines  are  crowded  together. 

Bores,  Paces,  and  Whirlpools  are  tidal  phenomena. 

Oceanic  currents  are  either  temporary,  periodical,  or 
constant. 

The  heat  of  the  sun  and  the  rotation  of  the  earth  are 
the  main  causes  of  constant  oceanic  currents. 

The  following  peculiarities  characterize  the  constant 
currents  in  the  three  central  oceans: 

(1.)  A  flow  in  the  equatorial  regions  from  the  east  to 
the  west; 

(2.)  A  flow  in  extra-tropical  regions  from  the  west  to 
the  east; 

(3.)  A  division  of  the  eastwardly  flowing  extra-tropical 
waters  in  mid-ocean  into  two  branches;  one  of  which 
flows  toward  the  poles,  and  the  other  toward  the  equator, 
where  it  merges  into  the  equatorial  currents. 


84 


PHYSICAL    GEOGRAPHY. 


The  principal  cause  of  constant  ocean  currents  is  the 
difference  in  the  density  of  the  equatorial  and  polar 
waters,  produced  by  differences  of  temperature. 

The  cold,  dense  waters  of  the  polar  regions  tend  to  mix 
with  the  warm,  light  waters  of  the  equatorial  regions 
along  due  north-and»-south  lines.  This  tendency  to  north 
and  south  direction  is  prevented  by  the  following  causes : 

(1.)  The  rotation  of  tho  earth  ; 

(2.)  The  position  of  the  continents: 

(3.)  The  direction  of  the  winds; 

(4.)  The  difference  in  the  saltness  of  the  water; 

(5.)  The  inequality  of  the  evaporation  and  rainfall. 


In  the  Pacific,  a  counter-current  crosses  the  ocean  in  the 
equatorial  region,  from  west  to  east. 

In  the  Indian  Ocean,  the  directions  of  the  currents  are 
modified  by  the  land  masses,  which  surround  the  northern 
part  of  its  bed. 

In  the  northern  hemispheres,  the  western  borders  of  the 
oceans  are  colder  than  the  eastern  borders  in  the  same  lati- 
tude, because  the  former  receive  the  polar  currents  and  the 
latter  the  equatorial. 

Currents  moderate  the  extremes  of  climate,  by  carry- 
ing the  warm  equatorial  waters  to  the  poles,  and  the  cold 
polar  waters  to  the  equator. 


REVIEW  QUESTIONS. 


-oottc 


How  much  heavier  is  salt  water  than  fresh  water  ? 

What  is  the  freezing-point  of  ocean  water? 

Explain  the  origin  of  the  saltness  of  the  oceanic  waters. 

In  the  equatorial  region,  where  is  the  water  the  colder, 
at  the  surface  or  near  the  bottom  of  the  ocean  ? 

How  do  the  areas  of  the  Pacific  and  Atlantic  compare 
with  each  other  in  size?    Of  the  Antarctic  and  Arctic? 

Define  inland  sea ;  border  sea ;  gulf  or  bay ;  fiord ;  give 
examples  of  each. 

Define  deeps ;  rises. 

What,  most  probably,  is  the  shape  of  the  bed  of  the  At- 
lantic?   Of  the  Pacific?    Of  the  Indian  Ocean  ? 

Describe  the  Telegraphic  Plateau. 

How  does  the  greatest  depth  of  the  ocean  compare  with 
the  greatest  elevation  of  the  land? 

Upon  what  does  the  height  of  a  wave  depend  ?  On  what 
does  its  velocity  depend? 

What  proof  is  there  that  during  wave  motion  in  deep 
water  there  is  no  continued  onward  motion  of  the  water? 

Distinguish  between  ebb  and  flood  tides. 

What  proofs  have  we  that  tides  are  occasioned  mainly 
by  the  attraction  of  the  moon  ? 

What  are  spring  tides?  Neap  tides?  During  what 
phases  of  the  moon  do  they  each  occur? 


Why  should  the  moon,  which  is  so  much  smaller  than 
the  sun,  exert  a  more  powerful  influence  in  producing 
tides  ? 

Where  does  the  parent  tidal  wave  originate  ? 

What  are  co-tidal  lines? 

Why  does  the  tidal  wave  progress  from  east  to  west  ? 

Explain  the  nature  of  the  influence  which  the  tidal 
wave  exerts  on  the  rotation  of'the  earth. 

In  what  parts  of  the  ocean  will  unusually  high  tides 
occur  ?    Why  ? 

By  what  are  races  and  whirlpools  occasioned? 

Distinguish  between  temporary,  periodical,  and  constant 
oceanic  currents. 

Explain  the  origin  of  constant  currents.  How  are  the 
directions  of  constant  currents  affected  by  the  rotation  of 
the  earth  and  the  shapes  of  the  continents  ? 

What  features  of  constant  currents  are  common  to  each 
of  the  three  central  oceans  ? 

On  which  side  of  the  northern  oceans  do.the  polar  cur- 
rents flow  ?    On  which  side  of  the  southern  oceans  ? 

What  are  sargasso  seas  ?    How  are  they  formed  ? 

What  effect  is  produced  by  ocean  currents  on  the  ex- 
tremes of  climate? 

Of  what  value  are  ocean  currents  to  navigation? 


MAP  QUESTIONS. 


K>XXC 


Point  out,  on  the  map  of  the  river-systems,  the  inland 
seas  of  the  Atlantic ;  of  the  Pacific ;  of  the  Indian  Ocean. 

Point  out  the  border  seas  of  the  Atlantic;  of  the 
Pacific. 

Point  out  the  gulfs  or  bays  of  the  Atlantic ;  of  the  In- 
dian Ocean. 

Point  out  the  principal  regions  of  fiords. 

How  many  hours  does  it  take  the  tidal  wave  to  progress 
from  Tasmania  to  the  Cape  of  Good  Hope  ?  From  Tasma- 
nia to  Newfoundland?  From  Tasmania  to  the  British 
Isles?    (See  map  of  the  co-tidal  lines.) 

In  what  parts  of  the  Atlantic  does  the  tidal  influence 
progress  most  rapidly? 

If  the  velocity  of  any  kind  of  wave  motion  in  water  in- 
creases with  the  depth  of  the  basin,  what  parts  of  the  At- 
lantic appear  to  be  the  deepest?  What  portions  of  the 
Pacific?    What  portions  of  the  Indian  Ocean? 

Trace  on  the  map  of  the  ocean  currents,  the  motion 
of  the  Antarctic  currents  in  each  of  the  three  central 
oceans. 


Where  is  the  Cape  Horn  current?  Is  it  hot  or  cold? 
What  points  of  resemblance  exist  between  the  north 
and  south  equatorial  currents  in  the  Atlantic  and  Pacific 
Oceans  ? 

Trace  the  progress  of  the  Gulf  Stream. 

What  points  of  resemblance  exist  between  the  Gulf 
Stream  and  the  Japan  current? 

How  far  to  the  north-east  do  the  waters  of  the  Gulf 
Stream  extend? 

What  distant  shores  are  warmed  by  the  waters  of  the 
Gulf  Stream?    By  those  of  the  Japan  current? 

Why  do  not  the  heated  waters  of  the  Gulf  Stream  exert 
a  more  powerful  influence  on  the  climate  of  the  eastern 
sea-board  of  the  United  States? 

Point  out  the  principal  cold  currents;  the  principal 
warm  currents. 

Which  currents  would  aid,  and  which  would  retard,  the 
progress  of  a  vessel  in  sailing  from  New  York  to  San  Fran- 
cisco? From  America  to  Europe?  From  America  to  India 
or  Australia? 


Part  IV. 

THE    ATMOSPHERE. 


o^Xc 


We  live  at  the  bottom  of  a  vast  ocean  of  air,  which,  like  the  ocean  of  water,  is  subject  to  three 
general  movements — waves,  tides,  and  currents.  By  means  of  waves,  its  upper  surface  is  heaved  in 
huge  mountain-like  masses  in  one  place,  and  hollowed  out  in  deep  valleys  in  another.  By  means  of 
currents,  circulatory  movements  are  set  up,  which  effect  a  constant  interchange  between  the  air  of  the 
equatorial  and  the  polar  regions.  By  means  of  tides,  the  depth  of  the  atmosphere  is  increased  in  some 
places  and  decreased  in  others. 

Of  these  three  movements  of  the  atmosphere,  currents  are  of  the  greatest  importance.  Aerial  cur- 
rents, or  winds,  are  similar  to  oceanic  currents,  but  are  more  extensive  and  rapid,  owing  to  the  greater 
mobility  of  air. 

By  retaining  and  modifying  the  solar  heat,  absorbing  and  distributing  moisture,  supplying  animals 
with  oxygen  and  plants  with  carbonic  acid,  the  atmosphere  plays  an  important  'part  in  the  economy 
of  the  earth. 

Meteorology  is  the  science  which  treats  of  the  atmosphere  and  its  phenomena. 


Section  I. 


THE   ATMOSPHERE. 


>o><Kc 


CHAPTER   I. 

General   Properties   of  the   Atmo- 
sphere. 

227.  Composition.  —  The  atmosphere  is  a  me- 
chanical mixture  of  nitrogen  and  oxygen,  in  the 


proportion,  by  weight,  of  nearly  77  per  cent,  of 
nitrogen  to  23  per  cent,  of  oxygen.  To  these 
must  be  added  a  nearly  constant  quantity  of  car- 
bonic acid,  about  5  or  6  parts  in  every  10,000 
parts  of  air,  or  about  a  cubic  inch  of  carbonic  acid 
to  every  cubic  foot  of  air,  and  a  very  variable  pro- 

85 


86 


PHYSICAL    GEOGRAPHY. 


portion  of  watery  vapor.  The  gaseous  ingredients, 
though  of  different  densities,  are  found  in  the 
same  relative  proportions  at  all  heights,  owing 
to  a  property  of  gases  called  diffusion. 

The  oxygen  and  carbonic  acid  are  the  most  important 
of  the  gaseous  constituents.  Oxygen  supports  combustion 
and  respiration,  and  is  thus  necessary  to  the  existence  of 
animal  life.  Carbonic  acid,  composed  of  carbon  and  oxy- 
gen, is  the  source  from  which  vegetation  derives  its  woody 
fibre,  and  is  thus  necessary  to  the  existence  of  plant  life. 
In  respiration,  animals  take  in  oxygen  and  give  out  car- 
bonic acid ;  in  sunlight,  plants  take  in  carbonic  acid  and 
give  out  oxygen.  In  this  way  the  relative  proportions  of 
the  substances  necessary  to  the  existence  of  animal  dnd  plant 
life  are  kept  nearly  constant. 

228.  Elasticity. — The  atmosphere  is  eminently 
elastic ;  that  is,  when  compressed,  or  made  to  oc- 
cupy a  smaller  volume,  it  will  regain  its  original 
volume  on  the  removal  of  the  pressure.  Air  also 
expands  when  heated  and  contracts  when  cooled. 

229.  Pressure. — So  evenly  does  the  atmosphere 
press  on  all  sides  of  objects  that  it  was  long  be- 
fore it  was  discovered  that  air  possesses  weight. 
The  discovery  was  made  by  Torricelli,  an  Italian 
philosopher  and  pupil  of  the  famous  Galileo.  The 
instrument  Torricelli  employed  is  called  a  Ba- 
rometer. 


Fig.  79.    Barometer. 

230.  The  Barometer.— The  principle  of  the  barometer 
is  as  follows :  A  glass  tube,  about  33  inches  in  length,  is 
closed  at  one  end  and  filled  with  pure  mercury.  Placing 
a  finger  over  the  open  end,  the  tube  is  reversed  and  dipped 
below  the  surface  of  mercury  in  a  cup  or  other  vessel. 
On  removing  the  finger,  a  column  of  mercury  remains  in 
the  tube,  being  sustained  there  by  the  pressure  of  the  at- 
mosphere. Near  the  sea-level  this  column  is  about  30 
inches  high ;  on  mountains  it  is  much  lower ;  in  all  cases, 
the  weight  of  the  mercurial  column  being  equal  to  that 
of  an  equally  thick  column  of  air,  extending  from  the 
level  of  the  reservoir  to  the  top  of  the  atmosphere. 

Any  variation  in  the  pressure  of  the  atmosphere  is 
marked  by  a  corresponding  variation  in  the  height  of  the 
mercury  in  the  barometer,  the  column  rising  with  in- 
creased, and  falling  with  diminished,  pressure. 

The  entire   atmosphere   presses  on  the   earth 


with  the  same  weight  as  would  a  layer  of  mer- 
cury about  30  inches  in  depth.  A  column  of 
mercury  30  inches  high,  and  one  square  inch  in 
area  of  cross  section,  weighs  about  15  pounds. 
Therefore,  the  pressure  which  the  atmosphere  exerts 
on  the  earth's  surface,  at  the  level  of  the  sea,  is  equal 
to  about  15  pounds  for  every  square  inch  of  surface. 
The  entire  weight  of  the  atmosphere,  in  pounds, 
is  equal  to  15  times  the  number  of  square  inches 
in  the  earth's  surface. 

The  atmospheric  pressure  is  not  uniform  on  all  parts  of 
the  earth  at  the  same  level.  From  a  few  degrees  beyond 
the  equator  the  pressure  increases  in  each  hemisphere  up 
to  about  lat.  35°,  where  it  reaches  its  maximum,  decreasing 
in  the  northern  hemisphere  to  lat.  65°,  when  it  again  in- 
creases toward  the  poles. 

231.  Height  of  the  Atmosphere. — If  the  air 
were  everywhere  of  the  same  density,  its  height 
could  be  easily  calculated ;  but,  on  account  of  its 
elasticity,  the  lower  layers  are  denser  than  the 
others,  because  they  have  to  bear  the  weight  of 
those  above  them.  The  density  must,  therefore, 
rapidly  dimiuish  as  we  ascend. 

If  by  pressure  on  a  gas  we  diminish  its  volume  one- 
half,  its  density  will  be  doubled;  conversely,  if  the  den- 
sity be  diminished  one-half,  the  volume  will  be  doubled. 
The  following  table,  calculated  from  the  law  of  increase 
in  volume  with  diminished  pressure,  gives  the  barometric 
height,  the  volume,  and  the  density  of  the  air  at  different 
elevations  above  the  sea.  The  elevation  of  3.4  miles  is  the 
result  of  observation ;  the  other  distances  are  estimated. 


Barometric 

Vol.  of  Given 

Density. 

Estimated  Distance 

Height  in  Inches. 

Weight  of  Air. 

al>.  Sea,  in  Miles. 

30.00 

1 

1 

0.0 

15.00 

2 

i 

3.4 

7.50 

4 

i 

6.8 

3.75 

8 

i 

10.2 

1.87 

16 

irV 

13.6 

.93 

32 

£ 

17.0 

It  appears  from  the  above  table  that  by  far  the 
greater  part  of  the  air  by  weight  lies  within  a  few 
miles  of  the  surface,  nearly  three-fourths  being 
below  the  level  of  the  summits  of  the  highest 
mountain-ranges. 

The  height  of  the  upper  limit  of  the  atmosphere 
has  been  variously  estimated.  Calculations  based 
upon  the  diminution  of  pressure  with  the  height, 
place  it  at  from  45  to  50  miles  above  the  level  of 
the  sea ;  others,  based  on  the  duration  of  twilight, 
place  it  at  distances  varying  from  35  to  200  miles. 

The  form  of  the  atmosphere  is  that  of  an  ob- 
late spheroid,  the  oblateness  of  which  is  greater 
than  that  of  the  earth. 


CLIMATE. 


87 


By  carefully  observing  the  decrease  in  pressure  with  the 
elevation,  at  different  altitudes,  and  making  proper  correc- 
tions, the  heights  of  mountains  can  be  readily  determined 
by  the  barometer.  The  measurement  of  heights  by  the 
barometer,  or  similar  means,  is  called  Hypsometry. 


>XX.c 


CHAPTER  II. 

Climate. 

232.  The  Climate  of  a  country  is  the  condi- 
tion of  its  atmosphere  as  regards  heat  or  cold. 

The  climate  of  a  country  also  embraces  the  con- 
dition of  the  air  as  regards  moisture  or  dryness, 
and  healthiness  or  unhealthiness,  which  are  de- 
pendent on  the  temperature. 

233.  Temperature. — The  temperature  of  the 
atmosphere  is  determined  by  means  of  an  instru- 
ment called  a  thermometer. 

The  thermometer  consists  of  a  glass  tube  of  very  fine 
bore,  furnished  at  one  end  with  a  bulb.  The  tube  is  care- 
fully dried  and  the  bulb  filled  with  pure  mercury  and 
heated  in  the  flame  of  a  spirit-lamp;  the  mercury  expands, 
and,  filling  the  fine  capillary  tube,  a  portion  runs  out 
from  the  open  end,  thus  effectually  expelling  the  air.  A 
blowpipe  flame  is  then  directed  against  the  open  end  and 
the  tube  hermetically  sealed.  As  the  bulb  cools,  the  mer- 
cury contracts,  and  leaves  a  vacuum  in  the  upper  part  of 
the  tube.  The  instrument  will  now  indicate  changes  in 
temperature;  for,  whenever  the  bulb  grows  warmer,  the 
column  of  mercury  expands  and  rises;  and  when  it  grows 
colder,  it  contracts  and  falls. 

In  order  to  compare  these  changes  of  level  they  are 
referred  to  certain  fixed  or  standard  points:  the  freezing- 
and  boiling-points  of  pure  water.  These  are  obtained  by 
marking  the  respective  heights  to  which  the  mercury  rises 
when  the  thermometer  is  plunged  into  melting  ice  and 
into  the  steam  escaping  from  boiling  water.  In  Fahren- 
heit's scale  the  freezing-point  is  placed  at  32°,  the  boil- 
ing-point at  212°,  and  the  space  between  these  two  points 
divided  into  180,  (212  — 32)  equal  parts,  called  degrees.  In 
the  Centigrade  scale  the  freezing-  and  boiling-points  are  re- 
spectively 0°  and  100°.  Fahrenheit's  degrees  are  repre- 
sented by  an  F.,  thus,  212°  F. ;  Centigrade's  by  a  C,  as 
100°  C. 

234.  Astronomical  and  Physical  Climates. — 
Astronomical  climate  is  that  which  would  result 
were  the  earth's  surface  entirely  uniform  and  of 
but  one  kind :  all  land  or  all  water. 

Physical  climate  is  that  which  actually  exists. 

Since  the  physical  climate  is  only  a  modification  of  the 
astronomical,  we  shall  briefly  review  the  causes  which 
tend  to  produce  a  regular  decrease  in  temperature  from 
the  equator  to  the  poles. 

Astronomical  Climate. — The  sun  is  practically 
the  only  source  of  the  earth's  heat.  On  account 
of  the  earth's  spherical  shape,  those  portions  of 


the  surface  are  most  powerfully  heated  which  re- 
ceive the  vertical  rays,  and  these  are  confined  to 
a  zone  reaching  23°  27'  on  each  side  of  the  equa- 
tor. Beyond  these  the  rays  fall  with  an  obliquity 
which  increases  as  we  approach  the  poles. 

235.  Causes  of  the  greater  heating  power  of 
the  vertical  rays  of  the  sun  than  of  the  oblique 
rays. 

lb       /«       I 


Fig.  80.    Causes  of  the  Greater  Heating  Power  of  the  Vertical 
than  of  the  Oblique  Kays, 

(1.)  The  vertical  rays  are  spread  over  a  smaller 
area.  Equal  areas  of  the  sun's  surface  give  off 
equal  quantities  of  heat.  If,  therefore,  the  bun- 
dle of  rays  a  b,  and  c  d,  come  from  equal  areas, 
the  amounts  of  heat  they  emit  will  be  equal ;  but 
while  the  heat  given  off  from  a  b,  the  more  ver- 
tical rays,  is  spread  over  the  earth's  surface  from 
/,  to  g,  that  from  c  d,  is  spread  over  the  greater 
area  h  i;  the  area  /  g,  therefore,  which  receives 
the  more  vertical  rays,  is  much  warmer  than  h  i, 
where  the  obliquity  is  greater. 

(2.)  The  vertical  rays  pass  through  a  thinner 
layer  of  air.  Only  a  part  of  the  sun's  heat 
reaches  the  surface  of  the  earth ;  about  28  per 
cent,  of  the  vertical  rays  are  absorbed  during  their 
passage  through  the  atmosphere.  The  amount  of 
this  absorption  must  increase  as  the  length  of 
path  increases.  In  the  figure,  the  light  shading 
represents  the  atmosphere.  It  is  clear  that  the 
oblique  rays  pass  through  a  thicker  stratum  of 
air  than  the  more  direct  ones,  and,  therefore,  are 
deprived  of  a  greater  amount  of  heat. 

According  to  Laplace,  the  thickness  of  the  stratum  of  air 
traversed  by  the  rays  when  the  sun  is  at  the  horizon  is 
35.5  times  greater  than  when  it  is  directly  overhead.  A 
similar  absorption  of  light  affects  the  comparative  bright- 
ness of  daylight  in  different  latitudes. 

(3.)  The  vertical  rays  strike  more  directly, 
and,  therefore,  produce  more  heat.     The  heating 


Page  88. 


CLIMATE. 


89 


power  of  the  more  nearly  vertical  rays  is  greater 
than  that  of  the  rays  which  strike  obliquely. 

236.  Variations  in  Temperature. — The  differ- 
ences in  the  heating  power  of  the  vertical  and  ob- 
lique rays  of  the  sun  cause  the  temperature  of 
the  earth's  surface  to  decrease  gradually  from  the 
equator  toward  the  poles.  The  differences  of  tem- 
perature thus  effected  are  further  increased  by  the 
difference  in  the  length  of  daylight  and  darkness. 
While  the  sun  is  shining  on  any  part  of  the  earth 
the  air  is  gaining  heat ;  when  it  is  not  shining  the 
air  is  losing  heat.  When  the  length  of  daylight 
exceeds  that  of  the  darkness,  the  gain  exceeds 
the  loss ;  when  the  darkness  exceeds  the  day- 
light, the  loss  exceeds  the  gain. 

The  excessively  low  temperatures  that  would 
result  from  the  oblique  rays  in  high  latitudes  are 
prevented  by  the  great  length  of  daylight  during 
the  short  summers,  thus  allowing  the  sun  to  con- 
tinue heating  the  surface  during  longer  periods. 
The  warmest  part  of  the  day  in  high  latitudes 
sometimes  equals  that  in  the  equatorial  regions. 
During  the  long  winters,  however,  the  continued 
loss  of  heat  makes  the  cold  intense. 

Hence  in  the  tropics  we  find  a  continual  sum- 
mer ;  in  the  temperate  zones,  a  summer  and  winter 
of  nearly  equal  length;  and  in  the  polar  zones, 
short,  hot  summers,  followed  by  long,  intensely  cold 
winters. 

The  true  temperature  of  the  air  is  ascertained  by  hang- 
ing a  thermometer  a  few  feet  above  the  ground,  so  as  to  be 
shielded  from  the  direct  rays  of  the  sun,  and  yet  be  in  free 
contact  on  all  sides  with  the  air. 

237.  Manner  in  which  the  Atmosphere  re- 
ceives its  Heat  from  the  Sun. — The  atmosphere 
receives  its  heat  from  the  sun —     . 

(1.)  Directly.  As  the  sun's  rays  pass  through 
the  air,  about  28  per  cent,  of  the  vertical  rays 
are  directly  absorbed,  thus  heating  the  air.  The 
remainder  pass  on  and  either  heat  the  earth,  or 
are  reflected  from  its  surface. 

(2.)  From  the  heated  earth.  The  sun's  rays 
heat  the  earth  and  the  heated  earth  heats  the  air. 
It  does  this  in  three  ways : 

(a.)  By  the  air  coming  in  contact  with  the 
heated  earth. 

(6.)  By  the  heated  earth  radiating  its  heat,  or 
sending  it  out  through  the  air  in  all  directions. 

After  the  sun's  heat  has  been  absorbed  by  the 
earth  and  radiated  from  it,  a  change  occurs  which 
renders  the  rays  much  more  readily  absorbed  by 
the  air. 

(c.)  By  the  heat  being  reflected  from  the  earth 
11 


and  again  sent  through  the  air.     But  little  heat 
is  imparted  to  the  air  in  this  way. 

It  is  mainly  the  aqueous  vapor  the  atmosphere 
contains  that  absorbs  the  sun's  heat.  Dry  air 
allows  the  greater  part  of  the  heat  to  pass  through 
it ;  therefore  variations  in  the  quantity  of  vapor  in 
the  air  must  necessarily  produce  corresponding 
variations  in  the  distribution  of  heat. 

238.  Isothermal  Lines  are  lines  connecting 
places  on  the  earth  which  have  the  same  mean 
temperature. 

The  Mean  Daily  Temperature  of  a  place  is  ob- 
tained by  taking  the  average  of  its  temperature 
during  twenty-four  consecutive  hours. 

The  Mean  Annual  Temperature  of  a  place  is 
the  average  of  its  mean  daily  temperature 
throughout  the  year. 

If  the  physical  climate  were  the  same  as  the 
astronomical,  the  isothermal  lines  would  coincide 
with  the  parallels  of  latitude. 

An  inspection  of  the  map  of  the  isothermal  lines  shows 
that  their  deviations  from  the  parallels,  though  well 
marked  ip  all  parts  of  the  earth,  are  greatest  in  the  north- 
ern hemisphere.  Wherever,  from  any  cause,  the  mean  tem- 
perature of  a  place  is  higher,  the  isothermal  lines  are  found 
nearer  the  poles;  ivhen  lower,  nearer  the  equator.  The  former 
effects  are  noticed  particularly  in  portions  of  the  ocean 
traversed  by  warm  currents ;  the  latter,  in  crossing  por- 
tions of  the  ocean  traversed  by  cold  currents.  In  the  map 
of  the  isothermal  lines  the  influence  of  elevation  is  re- 
moved by  adding  1°  for  every  1000  feet  of  elevation. 

239.  Physical  Zones.— The  Physical  Torrid 
Zone  lies  on  both  sides  of  the  equator,  between 
the  annual  isotherms  of  70°  Fahr. . 

The  Physical  Temperate  Zones  lie  north  and 
south  of  the  Physical  Torrid  Zone,  between  the 
annual  isotherms  of  70°  and  30°  Fahr. 

The  Physical  Frigid  Zones  lie  north  and  south 
of  the  Physical  Temperate  Zones,  from  the  an- 
nual isotherms  of  30°  Fahr.  to  the  poles. 

The  greatest  mean  annual  temperature  in  the 
eastern  hemisphere  is  found  in  portions  of  North 
Central  Africa,  and  in  Arabia  near  the  Red  Sea, 
in  the  southern  part  of  Hindostan,  and  in  the 
northern  part  of  New  Guinea  and  the  neighbor- 
ing islands;  in  the  western  hemisphere,  in  the 
northern  parts  of  South  America  and  in  Central 
America. 

240.  Modifiers  of  Climate.  —  The  principal 
causes  which  prevent  the  isothermal  lines  from 
coinciding  with  the  parallels  of  latitude  are: 

(1.)  The  Distribution  of  the  Land  and  Water 
Areas. — Land  heats  or  cools  rapidly,  absorbing  or 
emitting  but  little  heat.    This  is  because  the  land 


90 


PHYSICAL    GEOGRAPHY. 


has  a  small  capacity  for  heat,  and  also  because 
the  heat  passes  through  but  a  comparatively  thin 
layer.  Therefore,  a  comparatively  short  exposure 
of  land  to  heat  produces  a  high  temperature,  and 
a  comparatively  short  exposure  to  cooling,  a  low 
temperature.  Water  heats  or  cools  slowly,  ab- 
sorbing or  emitting  large  quantities  of  heat.  This 
is  because  water  has  a  great  capacity  for  heat. 
The  heat  penetrates  a  comparatively  deep  layer, 
and  then,  too,  as  soon  as  slightly  heated,  the  warm 
water  is  replaced  by  cooler  water.  Therefore,  the 
water  can  be  exposed  to  either  long  heating  or 
long  cooling  without  growing  very  hot  or  very 
cold.  Hence,  the  land  is  subject  to  great  and 
sudden  changes  of  temperature;  the  water,  to 
small  and  gradual  changes. 

Places  situated  near  the  sea  have,  therefore,  a 
more  equable,  uniform  climate  than  those  in  the 
same  latitude  in  the  interior  of  the  continent. 
The  former  are  said  to  have  an  oceanic  climate; 
the  latter,  a  continental  climate. 

In  the  polar  regions,  a  preponderance  of  moder~ 
ately  elevated  land  areas  causes  a  colder  climate  than 
an  equal  area  of  water,  because  land  loses  heat 
more  rapidly  than  water. 

In  the  tropics,  a  preponderance  of  land  areas^ 
causes  a  warmer  climate  than  an  equal  area  of  mUf, 
because  land  gains  heat  more  rapidly  than  water. 

(2.)  The  Distribution  of  the  Relief  Forms  of 
the  Land  Masses. 

(1.)  Elevation. — The  temperature  of  the  atmo- 
sphere rapidly  decreases  with  the  elevation.  The 
decrease  is  about  3°  Fahr.  for  every  1000  feet. 

The  increased  cold  is  caused  as  follows : 

(1.)  Since  the  air  receives  so  much  of  its  heat  indirectly 
from  the  earth's  surface,  the  farther  we  go  upward  from 
the  surface,  the  colder  it  grows. 

(2.)  In  the  upper  regions  of  the  atmosphere  the  de~ 
creased  density  and  humidity  of  the  air  prevent  it  from  ab- 
sorbing either  the  direct  rays  of  the  sun,  or  those  reflected 
or  radiated  from  the  earth.  The  effect  of  elevation  is  so 
powerful  that  on  the  sides  of  high  tropical  mountains  the 
same  changes  occur  in  the  vegetation  that  are  observed  in 
passing  from  the  equator  to  the  poles. 

(2.)  Direction  of  the  Slopes. — That  slope  of 
an  elevation  which  receives  the  sun's  rays  in  a 
direction  more  nearly  vertical  than  others,  will 
be  the  warmest. 

In  the  northern  hemisphere  the  southern  slope  of  a  hill 
is  warmer  in  winter  than  the  northern  slope,  because  it 
receives  the  rays  more  vertically. 

(3.)  Position  of  the  Mountain-Ranges.  —  A 
mountain-range  will  make  the  country  near  it 
warmer  if  the  wind  from  which  it  shields  it  is 


cold;   it  will   make   it  colder  if  such  wind  is 
warm. 

The  position  of  the  mountain-ranges  of  a  country  also 
greatly  affects  the  distribution  of  its  rainfall.  Thus,  the 
tropical  Andes  are  well  watered  and  fertile  on  their  east- 
ern slopes,  but  dry  and  barren  on  their  western.  The  pre- 
vailing moist  trade  winds,  forced  to  ascend  the  slopes, 
deposit  all  their  moisture  on  them  in  abundant  showers, 
and  are  dry  and  vaporless  when  they  reach  the  other  side. 

(4.)  Nature  of  the  Surface. — The  temperature 
of  a  tract  of  land  is  greatly  affected  by  the  nature 
of  its  surface.  If  covered  with  abundant  vege- 
tation, like  a  forest,  or  if  wet  and  marshy,  its  sur- 
face heats  and  cools  slowly,  and  has  a  compara- 
tively uniform  temperature ;  but  if  destitute  of 
vegetation,  and  dry,  sandy,  or  rocky,  it  both 
heats  and  cools  rapidly,  and  is  subject  to  great 
extremes  of  temperature. 

(3.)  Distribution  of  Winds  and  Moisture. — The 
principal  action  of  the  winds,  and  their  accom- 
panying moisture,  is  to  moderate  the  extremes  of 
temperature  by  the  constant  interchange  between 
the  heat  of  the  equatorial  and  the  cold  of  the 
polar  regions.  Both  wind  and  vapor  absorb  and 
render  latent  large  quantities  of  heat  in  the  equa- 
torial regions,  and  give  it  out,  in  higher  latitudes, 
on  cooling.  In  cold  countries  the  climate  is  ren- 
dered considerably  warmer  by  the  immense  quan- 
tity of  heat  thus  emitted  by  the  condensed  vapor. 

(4.)  Ocean  Currents. — Since  the  warm  waters 
move  to  the  polar  regions,  and  the  cold  waters  to 
the  equatorial  regions,  the  general  effect  of  ocean 
currents  on  climate  is  to  reduce  the  extremes  of 
temperature. 

The  combined  effects  of  the  action  of  the  winds, 
moisture,  and  ocean  currents  are  seen  in  the  north- 
ern continents,  whose  western  shores,  under  the  in- 
fluence of  the  prevailing  south-westerly  winds, 
copious  rains,  and  tropical  currents,  are  consider- 
ably warmer  than  the  eastern  shores  in  the  same 
latitude. 

The  coasts  of  Great  Britain  are  warm  and  fertile,  while 
Labrador,  in  the  same  latitude,  is  cold  and  sterile.  The 
island  of  Sitka,  in  the  Pacific,  is  warmer  than  Kamtchatka 
from  similar  causes. 


dXKc 


CHAPTER   III. 

The  Winds. 

241.  Origin  of  Winds. — Winds  are  masses  of 
air  in  motion.  They  resemble  currents  in  the 
ocean,  and  result  from  the  same  causes — differ- 


THE    WINDS. 


91 


ences  of  density  caused  by  differences  of  tem- 
perature. 

d  * 


A      A 

b 


J 


Fig,  81.    Origin  of  Winds. 


The  equilibrium  of  the  atmosphere  is  disturbed 
by  differences  of  temperature  as  fonows :  When 
any  area  becomes  heated,  as  at  a  a,  Fig.  81,  the 
air  over  it,  expanding  and  becoming  lighter,  is 
pressed  upward  by  the  colder  air  which  rushes 
in  from  all  sides.  Thus  result  the  following 
currents :  ascending  currents,  b  b,  over  the  heated 
area ;  lateral,  surface  currents,  c  c,  from  all  sides 
toward  the  heated  area;  upper  currents,  d  d,  from 
the  heated  area;  and  descending  currents,  e  e. 
It  is  the  lateral  currents  which  flow  toward  or 
from  the  heated  area  that  are  felt  mainly  as 
winds.  The  ascending  currents  rise  until  they 
reach  a  stratum  of  air  of  nearly  the  same  den- 
sity as  their  own,  and  then  spread  laterally  in 
all  directions  toward  the  areas  where  the  air 
has  been  rarefied  by  the  movements  of  the  lat- 
eral surface  currents,  until  they  finally  descend, 
and  recommence  their  motion  toward  the  heated 
area.  These  circulatory  motions  continue  as  long 
as  the  heated  area  remains  warmer  than  surround- 
ing regions. 

In  speaking  of  winds,  reference  is  always  made  to  the 
surface  currents,  unless  otherwise  stated. 

242.  Origin  of  the  Atmospheric  Circulation. — 
The  hottest  portions  of  the  earth  are,  in  general, 
within  the  tropics ;  hence  in  the  equatorial  regions 
ascending  currents  continually  prevail.  To  sup- 
ply the  partial  vacuum  so  created,  lateral  sur- 
face currents  blow  in  toward  the  equator  from 
the  poles,  while  the  ascending  currents,  after 
reaching  a  certain  elevation,  blow  as  upper  cur- 
rents toward  the  poles.  Thus  result  currents  by 
which  the  entire  mass  of  the  atmosphere  is  kept  in 
constant  circulation,  and  an  interchange  effected 
between  the  air  of  the  equator  and  the  poles. 

The  most  important  of  these  currents  are  the 
following : 

(1.)  Polar  currents,  or  the  lateral  surface  cur- 


rents, which  flow  from  the  poles  to  the  equator ; 
and 

(2.)  Equatorial  currents,  or  the  upper  currents, 
which  flow  from  the  equator  toward  the  poles. 

It  will  be  noticed  that  wherever  the  surface 
wind  blows  in  any  given  direction,  the  upper 
wind  blows  in  the  opposite  direction. 

In  several  instances  the  ashes  of  volcanoes  have  heen 
carried  great  distances  in  directions  opposite  to  that  in  which 
the  surface  wind  was  blowing.  The  smoke  from  tall  chim- 
neys at  first  takes  the  direction  of  the  surface  wind,  but 
rising,  is  soon  carried  in  the  opposite  direction  by  the 
upper  currents.  The  clouds  are  often  seen  moving  in  a 
direction  opposite  to  that  indicated  by  vanes  placed  on 
the  tops  of  the  houses. 

A  current  of  air  is  named  according  to  the  di- 
rection from  which  it  comes;  a  current  of  water, 
according  to  the  direction  in  which  it  .is  going. 
Thus,  a  north-east  wind  comes  from  the  north- 
east ;  a  north-east  current  of  water  goes  toward 
the  north-east. 

243.  Effect  of  the  Earth's  Rotation  on  the 
Direction  of  the  Wind. — Were  the  earth  at  rest, 
the  equatorial  and  polar  currents  would  blow  due 
north  and  south  in  each  hemisphere ;  but  by  the 
rotation  of  the  earth  they  are  turned  out  of  their 
course  in  a  manner  similar  to  the  oceanic  currents 
already  studied. 

The  polar  currents,  as  they  approach  the  equa- 
tor, where  the  axial  velocity  toward  the  east  is 
greater,  are  left  behind  by  the  more  rapidly  mov- 
ing earth,  and  thus  come,  as  shown  in  Fig.  83, 
from  the  north-east  in  the  northern  hemisphere, 
and  from  the  south-east  in  the  southern. 

The  equatorial  currents,  under  the  influence  of 
the  earth's  eastward  motion,  are  carried  toward 
the  east  as  they  approach  the  poles,  and  thus 
come,  as  shown  in  Fig.  83,  from  the  south-west  in 
the  northern  hemisphere,  and  from  the  north-west 
in  the  southern. 

Wherever  the  polar  winds  prevail,  their  direc- 
tion, when  unaffected  by  local  disturbances,  will 
be  north-east  in  the  northern  hemisphere,  and  south- 
east in  the  soidhern.  Near  the  equator  their  di- 
rection is  nearly  due  east. 

Wherever  the  equatorial  currents  prevail,  their 
direction  will  be  south-west  in  the  northern  hemi- 
sphere, and  north-west  in  the  southern. 

In  Fig.  82,  the  equatorial  currents  are  repre- 
sented as  continuing  to  either  pole  as  upper  cur- 
rents, and  the  polar  winds  as  surface  currents  to 
the  equator.  If  this  were  so,  constant  north-east- 
erly winds  would  prevail  in  the  northern  hemi- 


92 


PHYSICAL    GEOGKAPHY. 


'sa*. 


Fig.  82.    Direction  of  Wind  as  Affected  by  Rotation.         Fig.  83.    Interchange  of  the  Equatorial  and  Polar  Currents.    Wind  Zones, 


sphere,  and  constant  south-easterly  winds  in  the 
southern.  Several  causes,  however,  exist  to  pre- 
vent this  simple  circulation  of  the  air  between  the 
equatorial  and  polar  regions. 

The  equatorial  currents  do  not  continue  as  upper 
currents  all  the  way  to  the  poles,  but  fall  and  become 
surface  currents,  replacing  the  polar  winds,  which 
rise  and  continue  for  a  while  toward  the  equator  as 
upper  currents. 

244.  Causes  of  Interchange  of  Surface  and 
Upper  Currents. — The  causes  which  produce  this 
shifting  of  the  equatorial  and  polar  currents  are : 

(1.)  The  equatorial  currents  become  cold — 

(a.)  By  the  cold  of  elevation ; 

(b.)  By  expansion  ; 

(c.)  By  change  of  latitude. 

The  equatorial  currents  therefore  fall  and  are 
replaced  by  the  polar  currents,  which  have  been 
gradually  growing  warmer  by  continuing  near 
the  surface  of  the  earth. 

(2.)  As  the  equatorial  currents  approach  the 
poles  they  have  a  smaller  area  over  which  to 
spread,  and,  being  thereby  compressed,  are  caused 
to  descend  and  become  surface  currents. 

This  interchange  between  the  equatorial  and  polar  cur- 
rents takes  place  at  about  lat.  30°.  It  varies,  however, 
with  the  position  of  the  sun,  moving  toward  the  poles 
when  the  sUn  is  nearly  overhead,  and  toward  the  equator 
when  the  sun  is  in  the  other  hemisphere. 

The  interchange  in  the  position  of  the  equatorial  and 
polar  currents  is  represented  in  Fig.  83. 

As  the  equatorial  currrents  fall,  they  divide, 


part  going  to  the  poles,  and  part  returning  to  the 
equator. 

The  general  system  of  the  aerial  circulation 
thus  indicated  is  more  regular  over  the  oceans 
than  over  the  land.  Over  the  continents  the 
greater  heat  of  the  land  during  summer  causes 
a  general  tendency  of  the  wind  to  blow  toward 
the  land ;  similarly,  the  greater  cold  of  the  land 
during  winter  causes  a  tendency  of  the  wind  to 
blow  toward  the  sea. 

245.  Classification  of  Winds. — Winds  are  di- 
vided into  three  classes: 

(1.)  Constant,  or  those  whose  direction  remains 
the  same  throughout  the  year. 

(2.)  Periodical,  or  those  which,  for  regular  pe- 
riods, blow  alternately  in  opposite  directions. 

(3.)  Variable,  or  those  which  blow  in  any  di- 
rection. 

246.  Wind  Zones. — The  principal  wind  jzones 
are  the  zone  of  calms,  the  zones  of  the  trades,  the 
zones  of  the  calms  of  Cancer  and  Capricorn,  the 
zones  of  the  variable  winds,  and  the  zones  of  the 
polar  winds. 

Zone  of  Calms. — In  parts  of  the  ocean  near  the 
equator  the  ascending  currents  are  sufficiently 
powerful  to  neutralize  entirely  the  inblowing 
polar  currents,  and  thus  produce  a  calm,  which, 
however,  is  liable  at  any  moment  to  be  disturbed 
by  powerful  winds.  The  boundaries  of  the  zone 
vary  with  the  season ;  they  extend  from  about  2° 
to  11°  north  latitude. 


THE    WINDS. 


93 


Zones  of  the  Trades. — From  the  limits  of  the 
zone  of  calms  to  about  30°  on  each  side  of  the 
equator  the  polar  currents  blow  with  great  steadi- 
ness throughout  the  year.  The  constancy  in  their 
direction  has  caused  these  winds  to  be  named 
"  trade  winds,"  from  their  great  value  to  com- 
merce. Their  direction  is  north-east  in  the  north- 
ern hemisphere,  and  south-east  in  the  southern. 

Zones  of  the  Calms  of  Cancer  and  Capricorn. 
— Between  the  zones  of  the  trades  and  the  vari- 
ables, where  the  interchange  takes  place  between 
the  equatorial  and  polar  currents,  zones  of  calms 
occur.  Their  boundaries  are  not  well  defined, 
and  are  dependent  on  the  position  of  the  sun. 

Zones  of  the  Variable  Winds. — Beyond  the 
limits  of  the  preceding  zones  to  near  the  latitude 
of  the  polar  circles,  the  equatorial  and  polar  cur- 
rents alternately  prevail.  Here  the  equatorial 
and  polar  currents  are  continually  striving  for 
the  mastery,  sometimes  one  and  sometimes  the 
other  becoming  the  surface  current.  During 
these  conflicts  the  wind  may  blow  from  any 
quarter ;  but  when  either  current  is  once  estab- 
lished it  often  continues  constant  for  some  days. 
This  is  especially  the  case  over  the  ocean,  where 
the  modifying  influences  are  less  marked. 

Though  the  winds  in  these  zones  are  variable, 
still  two  directions  predominate :  south-west  and 
north-east  in  the  northern  hemisphere,  and  north- 
west and  south-east  in  the  southern.  Westerly 
winds,  however,  occur  the  most  frequently  in 
nearly  all  parts  of  these  zones. 

The  equatorial  currents  are  sometimes  called  the  Return 
Trades,  or  the  Anti-trades,  because  they  blow  in  the  oppo- 
site direction  to  the  trades. 

Between  about  lat.  25°  and  40°,  N.  and  S.,  over  parts  of 
the  ocean,  the  winds  are  nearly  periodical,  blowing  during 
the  hotter  portions  of  the  year  in  each  hemisphere  from 
the  poles,  and  during  the  remainder  of  the  year  from  the 
equator.  This  zone  is  often  called  the  Zone  of  the  Sub- 
tropical winds. 

Polar.  Zones. — From  the  limits  of  the  zones  of 
the  variables  to  the  poles,  there  are  regions  of  pre- 
vailing polar  winds.  These  winds  are  most  fre- 
quently north-east  in  the  northern  hemisphere, 
and  south-east  in  the  southern. 

247.  Dove's  Law  of  the  Rotation  of  the  Winds.— 
The  equatorial  and  polar  currents  usually  displace  each 
other,  and  become  surface  winds  in  a  regular  order,  first 
discovered  by  Prof.  Dove  of  Berlin. 

In  the  northern  hemisphere,  before  the  polar  current  is 
permanently  established  from  the  north-east,  the  wind 
blows  in  regular  order  from  the  west,  north-west,  and  north. 
The  displacement  of  the  polar  by  the  equatorial  currents 
occurs  in  the  opposite  direction :  from  the  east,  south-east, 


and  south,  before  the  general  south-west  current  is  perma- 
nently established. 

In  the  southern  hemisphere  these  motions  are  reversed. 

This  rotation  of  the  winds,  together  with  the  effects 
produced  on  the  thermometer  and  barometer,  is  indicated 
in  the  following  diagram.  Since  the  equatorial  currents 
are  warm,  moist,  and  light,  when  they  prevail  the  ther- 
mometer rises  and  the  barometer  falls.  On  the  establish- 
ment of  the  polar  currents,  however,  the  thermometer 
falls  and  the  barometer  rises. 


NORTHERN  HEMISPHERE 

N. 


SOUTHERN  HEMISPHERE. 

N. 


Fig.  84.    Rotation  of  the  Winds  (after  Dove). 

The  "  warm  waves  "  of  the  zones  of  the  variable 
winds  are  caused  by  the  prevalence  of  the  equa- 
torial currents.  Similarly,  the  "  cold  waves  "  are 
caused  by  the  prevalence  of  the  polar  currents. 

248.  Land  and  Sea  Breezes. — During  the  day 
the  land  near  the  coast  becomes  warmer  than  the 
sea.  An  ascending  current,  therefore,  rises  over 
the  land,  and  a  breeze,  called  the  sea  breeze,  sets 
in  from  the  sea.  At  night  the  land,  from  its 
more  rapid  cooling,  soon  becomes  colder  than  the 
water ;  the  ascending  current  then  rises  from  the 


Fig,  85.    Land  and  Sea  Breezes. 

water,  and  a  breeze,  called  the  land  breeze,  sets  in 
from  the  land.  The  strength  of  these  winds  de- 
pends upon  the  difference  in  the  temperature  of 
the  land  and  water ;  they  are,  therefore,  best  de- 
fined in  the  tropical  and  extra-tropical  regions, 
though  they  may  occur  in  higher  latitudes  during 
the  hottest  parts  of  the  year.  Land  and  sea 
breezes  are  periodical  winds. 
N^  249.  Monsoons  are  periodical  winds,  which  dur- 
ing part  of  the  year  blow  with  great  regularity  in 
one  direction,  and  during  the  remainder  of  the 


Page  94 


THE    WINDS. 


95 


year  in  the  opposite  direction.  They  are  in  real- 
ity huge  land  and  sea  breezes,  caused  by  the  dif- 
ference in  temperature  between  the  warmer  and 
colder  halves  of  the  year.  They  occur  mainly  in 
the  regions  of  the  trades,  and  are  in  reality  trade 
winds  which  have  been  turned  out  of  their  course 
by  the  unequal  heating  of  land  and  water. 

During  winter,  in  either  hemisphere,  the  oceans, 
being  warmer  than  the  land,  cause  a  greater 
regularity  in  the  trades;  but  during  summer,  the 
tropical  continents  become  intensely  heated,  and 
their  powerful  ascending  currents  cause  the  equa- 
torial currents  to  blow  toward  the  heated  areas 
as  surface  winds,  and  thus  displace  the  trades. 
The  interval  between  the  two  monsoons  is  gener- 
ally characterized  by  calms,  suddenly  followed  by 
furious  gales,  that  may  blow  from  any  quarter. 

250.  Monsoon  Regions. — There  are  three  well- 
marked  regions  of  monsoons — the  Indian  Ocean, 
the  Gulf  of  Guinea,  and  the  Mexican  Gulf  and 
Caribbean  Sea.  The  first  is  the  largest  and  most 
distinctly  marked. 

Monsoons   of  the   Indian   Ocean.  —  Here  the 


trades  are  deflected  by  the  overheating  of  the 
continents  of  Asia,  Africa,  and  Australia. 

In  the  northern  hemisphere  the  north-east  trades  prevail 
with  great  regularity  over  the  Indian  Ocean  during  the 
cooler  half  of  the  year :  from  October  to  April,  but  during 
the  warmer  half:  from  April  to  October,  the  heated  Asiatic 
continent  deflects  the  trades,  and  the  equatorial  currents 
prevail  from  the  south-west.  The  same  winds  also  pre- 
vail south  of  the  equator,  on  the  western  border  of  the 
ocean,  along  the  eastern  coast  of  Africa  as  far  south  as 
Madagascar. 

In  the  southern  hemisphere,  in  the  south-eastern  portion 
of  the  ocean,  the  south-east  trade  is  similarly  deflected  by 
the  Australian  continent.  Here  the  winds  blow  south- 
east during  the  southern  winter,  and  north-west  during 
its  summer. 

Monsoons  of  the  Gulf  of  Guinea. — Here  the 
north-east  trades  are  deflected  by  the  intensely 
heated  continent  of  Africa.  The  south-west  sum- 
mer monsoon  blows  over  the  land  as  far  inland 
as  the  Kong  Mountains. 

Monsoons  of  the  Mexican  Gulf  and  Caribbean 
Sea. — In  this  region  the  north-east  trade  winds 
are  deflected  by  the  overheating  of  the  Missis- 
sippi Valley.  The  Northers  of  Texas,  which  are 
cold  winds  blowing  for  a  few  days  at  a  time  over 
the  Texan  and  Mexican  plains,  may  be  considered 
as  connected  with  the  winter  monsoons. 

Besides  the  preceding  well-marked  regions,  nearly  all 
the  coasts  of  the  continents  in  and  near  the  tropics  have 
small  monsoon  regions,  as,  for  example,  the  western  coasts 
of  Mexico,  the  eastern  and  western  coasts  of  South  Amer- 
ica, and  the  western  and  northern  coasts  of  Africa. 


>t  • 


251.  Desert  Winds. — The  rapid  heating  and 
cooling  of  deserts  make  them  great  disturbers 
of  the  regular  system  of  winds.  Currents  al- 
ternately blow  toward  and  from  the  heated  area. 
The  latter  are  intensely  hot  and  dry. 

The  Etesian  Winds. — During  summer  the  barren 
soil  of  the  Desert  of  Sahara,  becoming  intensely 
heated,  causes  strong  north-east  winds  to  blow 
from  the  north  over  the  Mediterranean  Sea, 
These  are  called  the  Etesian  winds,  and  continue 
from  July  to  September ;  they  are  strongest  dur- 
ing the  daytime. 

Hot  Desert  Winds. — From  the  Sahara  a  period- 
ical wind,  called  the  Harmattan,  blows  on  the  soidh- 
west,  over  the  coasts  of  Guinea ;  on  the  north,  the 
Solano  blows  over  Spain,  and  the  Sirocco  blows 
over  Southern  Italy  and  Sicily.  Though  some- 
what tempered  during  their  passage  across  the 
Mediterranean,  these  winds  are  still  exceedingly 
hot  and  oppressive. 

From  the  deserts  of  Nubia  and  Arabia  in- 
tensely hot,  dry  winds  blow  in  all  directions  over 
the  coasts  of  Arabia,  Nubia,  Persia,  and  Syria. 
These  winds  are  known  under  the  general  name 
of  the  simoom  or  samiel.  From  their  high  tem- 
perature and  the  absence  of  moisture,  they  often 
cause  death  from  nervous  exhaustion. 

During  the  prevalence  of  the  simoom,  particles  of  fine 
sand  are  carried  into  the  atmosphere  and  obscure  the  light 
of  the  sun.  Becoming  intensely  heated,  these  particles, 
by  their  radiation,  increase  the  temperature  of  the  air, 


Fig.  86,    Sand  Storm  in  the  Desert. 


which  sometimes  rises  as  high  as  120°  or  130°  Fahr.  When 
powerful  winds  prevail,  dense  clouds  of  sand  are  carried 
about  in  the  atmosphere,  producing  the  so-called  sand 
storms.  The  sand-drifts  which  are  thus  formed  constantly 
change  their  position. 


96 


PHYSICAL    GEOGRAPHY. 


The  Khamsin  blows  at  irregular  intervals  over 
Egypt  from  the  south ;  but  when  established, 
generally  continues  for  fifty  days.  It  is  intensely 
hot  and  dry,  like  the  simoom,  and  is  loaded  with 
fine  sand. 

252.  Mountain  Winds. — During  the  day  the 
elevated  slopes  of  mountains  heat  the  air  over 
them  hotter  than  at  corresponding  elevations  over 
the  valleys.  Currents,  therefore,  ascend  the  val- 
leys toward  the  mountains  during  the  day.  During 
the  night,  however,  the  air  near  the  summits  be- 
comes colder  than  that  near  the  base.  Currents, 
therefore,  descend  the  valleys  from  the  mountains 
during  the  night. 

oo^oo 

CHAPTER   IV. 

Storms. 

253.  Storms  are  violent  disturbances  of  the 
ordinary  equilibrium  of  the  atmosphere  by  wind, 
rain,  snow,  hail,  or  thunder  and  lightning. 

During  storms  the  wind  varies  in  velocity  from 
that  of  a  scarcely  perceptible  breeze  to  upwards 
of  200  miles  per  hour. 

Velocity  and  Power  op  Winds. 


Velocity  of  Wind  in 
Miles,  per  hour. 

Common  Names  of  Winds. 

1 
4  to  5 

Hardly  Perceptible  Breeze. 
Gentle  Wind. 

10  to  15 

Pleasant  Brisk  Gale. 

20  to  25 
30  to  35 

40 

50 

Very  Brisk. 
High  Wind. 
Very  High. 
Storm. 

60 

Great  Storm. 

80 

Hurricane. 

100 

Violent  Hurricane. 

80  to  200 

Tornado. 

254.  Cyclones  are  storms  of  considerable  ex- 
tent, in  which  the  velocity  of  the  wind  is  much 
greater  than  usual,  and  the  air  moves  in  eddies  or 
whirls,  somewhat  similar  to  whirlwinds,  but  of 
vastly  greater  power  and  diameter. 

In  all  such  storms  the  wind  revolves  around  a 
calm  centre ;  over  the  calm  centre  the  barometer 
is  low,  but  on  the  sides,  and  especially  on  that  side 
toward  which  the  storm  is  moving,  it  is  high. 

Besides  the  rotary  motion  of  the  wind,  there  is 
also  a  progressive  motion,  which  causes  the  storm 
to  advance  bodily,  moving  rapidly  in  a  parabolic 
path.  The  general  term  Cyclone  has  been  ap- 
plied to  these  storms  on  account  of  their  rotary 
motion.     They  have  also  various  local  names. 


Cyclones  originate  in  the  tropical  regions,  but 
frequently  extend  far  into  the  temperate  zones. 


Fig.  87.  A  Storm  at  Sea. 

255.  Regions  of  Cyclones. — The  following  are 
the  most  noted  regions : 

The  West  Indies,  where  they  are  generally 
called  hurricanes. 

The  China  Seas,  where  they  are  known  as 
typhoons. 

The  Indian  Ocean. 

In  each  of  these  regions  the  storms  occur  about 
the  time  of  the  change  of  the  regular  winds,  and 
have  their  origin  in  marked  differences  of  tem- 
perature ;  thus  in  the  Indian  Ocean  and  the  China 
Seas,  they  generally  occur  at  the  change  of  the  mon- 
soon, after  the  great  heat  of  summer.  They  are  at- 
tended with  the  condensation  of  moisture  and  in- 
tense electrical  disturbance. 

256.  Cause  of  Cyclones. — Cyclones  originate  in 
an  area  of  low  barometer  caused  by  the  ascending 
current  of  air  that  follows  the  overheating  of  any 
region.  As  the  air  rushes  in  from  all  sides  it  is 
deflected  by  the  earth's  rotation,  and  assumes  a 
rotary  or  whirling  motion  around  the  heated  area. 
The  centrifugal  force  generated  by  this  rotation 
causes  the  barometric  pressure  of  the  area  to  be- 
come lower  and  the  area  to  grow  larger.  Mean- 
while the  inflowing  air,  ascending,  is  chilled  by 
the  cold  of  elevation  and  by  expansion  sufficiently 
to  condense  its  vapor  rapidly.  The  heat  energy, 
previously  latent  in  the  vapor,  is  now  disengaged, 
and  causes  the  air  to  mount  higher  and  condense 
still  more  of  its  vapor.  It  is  to  the  energy  thus 
rapidly  liberated  by  the  condensation  of  the  vapor 
that  the  violence  of  the  cyclone  is  due.  Cyclones, 
therefore,  acquire  extraordinary  violence  only 
when  an  abundance  of  vapor  is  present  in  the 
air. 


STORMS. 


97 


As  the  inblowing  winds  come  near  the  heated 
area,  they  must  blow  with  increased  violence  in 
order  to  permit  the  same  quantity  of  air  to  pass 
over  the  constantly  narrowing  path. 

Besides  the  rotary  motion  of  the  wind,  the 
storm  moves  or  progresses  over  a  parabolic  path, 
which  in  the  tropics  is  generally  toward  the  west, 
and  in  the  temperate  zones  toward  the  east.  This 
progressive  motion  of  the  storm  is  like  the  similar 


January 


Fig.  88.    Chart  showing  Path  and  Direction  of  Cyclone, 

motion  often  noticed  in  a  rapidly  spinning  top. 
It  is  due  to  the  combined  influences  of  the  inrush 
of  air,  the  earth's  rotation,  and  centrifugal  force. 
257.  Peculiarities  of  Cyclones. — Cyclones  rage 
most  furiously  in  the  neighborhood  of  islands  and 
along  the  coasts  of  continents.  They  are  most 
powerful  near  their  origin.  As  they  advance  the 
spiral  increases  in  size  and  the  fury  of  the  wind 
gradually  diminishes,  because  the  amount  of  moist- 
ure in  the  air  is  less.     The  rotarv  motion  varies 


from  30  to  100  miles  an  hour.  The  progressive 
motion  of  the  calm  centre  is  more  moderate — 
from  20  to  50  miles  an  hour.  This  progressive 
motion  is  least  in  the  tropics  and  greatest  in  the 
temperate  regions. 

The  wind  invariably  rotates  in  the  same  direc- 
tion in  each  hemisphere ;  in  the  northern,  it  ro- 
tates from  right  to  left,  or  in  the  direction  oppo- 
site to  that  of  the  hands  of  a  watch  ;  in  the  south- 
ern, from  left  to  right,  or  in  the  same  direction  as 
the  hands  of  a  watch.     The  cause  of  the  regu- 


NOBTHBEN  HEMISPHERE. 


\ 


I 


/ 


'*I*\  01  y^ 


SOUTHERN  HEMISPHERE. 


/ 


\ 


\ 


/ 


V.    -4--... 


*1{%\1  o\ 


/ 


I 


X 


Fig.  89.    Canse  of  the  Rotation  of  the  Wind. 

larity  of  rotation  is  seen,  from  an  inspection  of 
Fig.  89,  to  be  due  to  the  rotation  of  the  earth. 
The  wind,  blowing  in  from  all  sides  toward  the 
heated  area,  is  so  deflected  by  the  rotary  motion 
of  the  earth  as  to  move  in  vast  circles,  from  right 
to  left  in  the  northern  hemisphere,  and  from  left 
to  right  in  the  southern. 

The  force  of  the  wind  in  these  storms  is  tremendous. 
So  furiously  does  the  wind  lash  the  water  that  its  tem- 
perature is  often  sensibly  raised  by  the  friction. 

The  intelligent  navigator  always  endeavors  to  avoid  the 
centre  of  the  storm,  since  it  is  the  most  dangerous  part. 
This  he  can  do  by  remembering  the  direction  of  the  rota- 
tion of  the  wind  in  the  hemisphere  he  may  be  in ;  for  if, 
in  the  northern  hemisphere,  he  stands  so  that  the  wind 
blows  directly  in  his  face,  the  calm  centre  is  on  his  right, 
while  in  the  southern  hemisphere  it  is  on  his  left;  and  in- 
stead of  running  with  the  storm,  hoping  to  outsail  it,  he 
will  boldly  steer  toward  its  circumference. 

258.  Tornadoes  and  Whirlwinds  are  the  same 
as  cyclones,  except  that  they  are  more  limited  in 
area.   Their  violence,  however,  often  exceeds  that 


-# 


98 


PHYSICAL    GEOGRAPHY. 


of  cyclones.  Tornadoes  appear  to  be  due  to  ro- 
tary motion  of  the  air  occurring  above  the  earth's 
surface,  which  results  in  a  rapid  sucking  up  of  the 
warmer  surface  air. 

259.  Water-spouts. — When  tornadoes  or  whirl- 
winds occur  on  the  water  they  cause  a  water-spout. 
A  rapid  condensation  of  vapor  takes  place,  both 
from  the  different  temperature  of  the  winds  and 
from  the  rarefaction  produced  at  the  centre  of  the 
revolving  mass  of  air. 

Portions  of  the  clouds  are  sometimes  drawn 
down  from  above  and  whirled  around  in  the 
form  of  an  immense  funnel-shaped  mass ;  finally 
the  whirl  reaches  the  water,  and  a  column  of 
spray  is  thrown  up,  which  unites  with  the  mass 
above  and  moves  over  the  surface  of  the  water 
as  an  immense  pillar.  Though  of  formidable  ap- 
pearance, water-spouts  have  never  been  known 
seriously  to  damage  large  vessels. 

Similar  phenomena  are  noticed  on  the  land 
when  tornadoes  occur.  Here,  however,  only  the 
cloud  cone  is  observed. 

260.  The  North-Easters  and  other  Storms  of 
the  United  States. — The  following  important  facts 
have  been  discovered  in  regard  to  the  extended 
storms  which  occur  in  the  United  States: 

(1.)  All  our  great  storms  are  attended  by  an 
immense  whirling  of  the  wind,  and  are,  in  fact, 
species  of  cyclones. 

(2.)  The  great  north-east  storms  of  our  eastern 
sea-board  originate  in  the  west,  in  an  area  of  low 
barometer,  somewhere  between  Texas  and  Minne- 
sota. In  the  front  and  rear  of  this  area  the  ba- 
rometer is  high. 

(3.)  The  calm  centre  of  the  storm,  or  the  area 
of  low  barometer,  moves  toward  the  north-east. 
The  shape  of  the  calm  centre  is  longer  from 
north  to  south  than  from  east  to  west. 


(4.)  The  storms  begin  by  the  winds  blowing 
toward  the  area  of  low  barometer. 

(5.)  During  the  prevalence  of  the  storm  the 
winds  are  north-east,  east,  or  south-east ;  toward 
the  end,  north-west,  west,  and  south-west. 

261.  Sailing  Routes. — A  knowledge  of  the  di- 
rections of  the  winds  and  ocean  currents  has  ma- 
terially diminished  the  time  required  by  sailing 
vessels  to  go  from  one  port  to  another.  Opposing 
winds  and  currents  often  render  it  advisable  for  the 
vessel  to  begin  its  journey  in  a  direction  consider- 
ably out  of  the  direct  line  of  the  desired  port. 

Europe— America.— The  Gulf  Stream  and  prevailing 
westerly  winds  render  the  passage  across  the  ocean  from 
east  to  west  considerably  longer  than  from  west  to  east. 
The  general  route,  in  either  direction,  varies  with  the 
season  of  the  year. 

New  York  —  San  Francisco. — After  leaving  New 
York  the  course  is  considerably  to  the  east,  in  order  to 
clear  the  South  American  coast  in  the  region  of  the  trades. 
After  doubling  Cape  Horn  the  course  is  westward.  The 
zone  of  the  north-east  trades  is  entered  about  118°  W. 
long. 

America— India— Australia.— In  sailing  from  Amer- 
ica to  India  or  Australia  the  vessel  takes  the  same  route 
as  between  Eastern  America  and  San  Francisco.  About 
opposite  Eio  Janeiro,  however,  the  routes  diverge.  On 
entering  the  Indian  Ocean  the  direction  is  dependent  on 
that  of  the  prevailing  monsoon. 

Europe— India— Australia.— The  vessels  either  pass 
through  the  Mediterranean  Sea  and  the  Suez  Canal,  or 
around  the  Cape  of  Good  Hope.  The  broad  expanse  of 
ocean  in  the  southern  hemisphere,  in  the  zone  of  the  vari- 
ables, renders  the  westerly  winds  very  steady.  Vessels  sail- 
ing from  Atlantic  ports  of  America  or  Europe  generally 
find  it  preferable  to  go  by  the  eastward  route,  around  the 
Cape  of  Good  Hope,  and  return  by  the  westward  route, 
around  Cape  Horn,  thus  circumnavigating  the  globe. 

California — Japan. — The  southerly  route,  from  east  to 
west,  is  aided  by  the  north-east  trades  and  the  north  equa- 
torial current  of  the  Pacific ;  the  northerly  route,  from 
west  to  east,  is  necessary  in  order  to  avoid  the  trade 
winds. 

The  general  sailing  routes  between  some  of  the  most 
important  ports  are  traced  on  the  map  of  the  winds. 


SYLLABUS. 


—o^c 


Atmospheric  air  is  composed  mainly  of  a  mixture  of  ni- 
trogen and  oxygen,  in  the  proportion,  by  weight,  of  about 
77  parts  of  nitrogen  to  23  of  oxygen  in  every  hundred 
parts.  The  atmosphere  also  contains  small  quantities  of 
carbonic  acid  and  the  vapor  of  water. 

The  oxygen  of  the  air  is  necessary  to  combustion  and 
respiration ;  the  carbonic  acid  and  the  vapor  of  water,  to 
plant-life. 

At  the  level  of  the  sea  the  atmosphere  presses  on  every 
square  inch  of  the  earth's  surface  with  a  force  of  about  15 
pounds. 


The  upper  limit  of  the  atmosphere  has  been  variously 
estimated  at  from  50  to  200  miles  above  the  level  of  the 
sea. 

A  barometer  is  used  for  measuring  the  pressure  of  the  at- 
mosphere ;  a  thermometer,  for  measuring  its  temperature. 

The  vertical  rays  of  the  sun  are  warmer  than  the  oblique 
rays — 1.  Because  they  are  spread  over  a  smaller  area  of  the 
earth.  2.  Because  they  pass  through  a  thinner  stratum  of 
air,  and  consequently  lose  less  of  their  heat  by  absorption. 
3.  Because  they  strike  the  earth  more  directly,  and  there- 
fore produce  more  heat. 


REVIEW    QUESTIONS. 


99 


Continual  summer  is  found  in  the  tropics ;  summer  and 
winter  of  nearly  equal  length  in  the  temperate  zones; 
short,  hot  summers,  followed  by  intensely  cold  winters,  in 
the  polar  zones. 

The  atmosphere  is  heated — 1.  Either  by  direct  absorp- 
tion of  the  rays  while  passing  through  it;  or  2.  By  con- 
tact with,  or  by  radiation  and  reflection  from,  the  heated 
earth. 

Isothermal  lines  connect  places  whose  mean  temperature 
is  the  same. 

The  mathematical  zones  are  bounded  by  the  parallels 
of  latitude;  the  physical  zones,  by  the  isotherms. 

The  mathematical  and  physical  zon«s  do  not  coincide — 
1.  Because  of  the  unequal  distribution  of  the  land  and 
water  areas.  2.  The  irregularities  in  the  surface  of  the 
land.  3.  The  distribution  of  the  winds  and  moisture.  4. 
The  ocean  currents.    5.  The  difference  in  the  rainfall. 

The  temperature  of  the  air  decreases  with  the  altitude 
— 1.  Because  the  air  receives  most  of  its  heat  from  the 
earth's  surface,  so  that  it  must  grow  continually  colder  the 
farther  we  go  above  the  surface.  2.  The  decreased  den- 
sity and  humidity  of  the  air  prevent  it  from  absorbing 
either  the  direct  rays  of  the  sun  or  those  reflected  or  ra- 
diated from  the  earth. 

Places  situated  near  the  sea  have  a  more  equable,  uni- 
form climate  than  those  in  the  same  latitude  in  the  inte- 
rior of  the  continent. 

Whenever  any  part  of  the  earth's  surface  is  heated  more 
than  the  neighboring  parts,  ascending  currents  occur  over 
the  heated  area,  lateral  surface  currents  blow  in  toward 
the  heated  area,  and  upper  currents  blow  from  the  heated 
area. 

The  general  system  of  the  atmospheric  circulation  con- 
sists mainly  of  the  following  currents :  1.  The  polar  cur- 
rents, blowing  from  the  poles  toward  the  equator.  2.  The 
equatorial  currents,  blowing  from  the  equator  toward  the 
poles. 

The  direction  of  these  currents  is  modified  by  the  rota- 
tion of  the  earth.  Thus  modified,  the  equatorial  currents 
are  south-west  in  the  northern  hemisphere,  and  north- 
west in  the  southern.  The  polar  currents  are  north-east 
in  the  northern  hemisphere,  and  south-east  in  the  south- 
ern. 


When  a  wind  at  the  surface  blows  in  any  direction,  there 
is  generally  an  upper  current  blowing  in  the  opposite  di- 
rection. 

The  equatorial  currents  do  not  continue  as  upper  cur- 
rents to  the  poles — 1.  Because  they  become  cooled  and  fall. 
2.  From  the  contracted  space  of  the  higher  latitudes  when 
compared  with  that  of  the  equator. 

We  distinguish  the  following  wind  zones:  the  zone  of 
calms ;  the  zones  of  the  trades ;  the  zones  of  the  calms  of 
Cancer  and  Capricorn ;  the  zones  of  the  variables ;  and  th« 
zones  of  the  polar  winds. 

Land  and  sea  breezes  are  caused  by  the  unequal  heating 
of  the  land  and  water  during  day  and  night;  monsoons, 
by  their  unequal  heating  during  summer  and  winter. 

Monsoons  occur  on  the  coasts  of  tropical  countries  within 
the  limits  of  the  trade  zones.  They  are  most  frequent  in 
the  Indian  Ocean,  in  the  Gulf  of  Guinea,  and  in  the  Mex- 
ican Gulf  and  neighborhood. 

The  Etesian  Winds  blow  over  the  Mediterranean  toward 
the  Desert  of  Sahara. 

The  Hot  Winds  caused  by  the  deserts  of  Sahara  and 
Arabia  are  the  Harmattan,  over  Guinea;  the  Solano,  over 
Spain ;  the  Sirocco,  over  Italy ;  the  Simoom,  over  Arabia, 
Nubia,  and  Persia;  and  the  Khamsin,  over  Egypt. 

In  most  mountainous  regions  winds  blow  up  the  valleys 
toward  the  mountains  during  the  day,  and  down  the  val- 
leys from  the  mountains  during  the  night. 

Cyclones  are  caused  by  the  wind  blowing  in  from  all 
sides  toward  an  area  of  low  barometer  caused  by  the 
overheating  of  the  area.  The  centrifugal  force  thus  gen- 
erated increases  both  the  size  of  the  area  and  the  differ- 
ence of  pressure  as  compared  with  regions  surrounding 
it.  The  fury  of  the  storm  is  increased  by  the  heat  energy 
liberated  by  the  condensation  of  the  vapor  in  the  uprush- 
ing  air. 

Storms  occur  whenever  the  ordinary  equilibrium  of  the 
atmosphere  is  violently  disturbed  by  wind,  rain,  snow, 
hail,  or  thunder  and  lightning. 

Nearly  all  powerful  storms  are  attended  with  a  rotation 
of  the  wind.  Such  storms  are  known  under  the  general 
names  of  Cyclones,  Hurricanes,  Typhoons,  and  Tornadoes. 

The  north-easters  and  other  great  storms  of  the  United 
States  are  species  of  cyclones. 


REVIEW   QUESTIONS. 


-oo^c 


Of  what  use  is  the  atmosphere  in  the  economy  of  the  earth  ? 

Define  meteorology. 

Describe  the  construction  of  a  barometer. 

What  proof  have  we  that  the  greater  part  of  the  atmo- 
sphere, by  weight,  lies  within  a  few  miles  of  the  earth's 
surface? 

Define  hypsometry. 

Describe  the  construction  of  a  thermometer. 

Why  are  the  vertical  rays  of  the  sun  warmer  than  the 
oblique  rays? 

What  is  the  characteristic  climate  of  the  tropics?  Of 
the  temperate  regions?    Of  the  polar  regions? 

In  what  different  ways  does  the  atmosphere  receive  its 
heat  from  the  sun  ? 

State  the  boundaries  of  the  mathematical  torrid  zone. 
Of  the  physical  torrid  zone.    Of  the  mathematical  and 
physical  temperate  zones.     Of  the  mathematical  and  phys- 
ical frigid  zones. 
12 


In  what  parts  of  the  eastern  hemisphere  is  the  greatest 
mean  annual  temperature  found?  In  what  parts  of  the 
western  hemisphere? 

What  influence  is  produced  on  the  climate  of  high  lati- 
tudes by  a  preponderance  of  moderately  elevated  land 
masses?    On  the  climate  of  the  tropics? 

Why  should  the  temperature  of  the  atmosphere  decrease 
with  the  altitude  ? 

Name  all  the  causes  which  prevent  the  mathematical 
climatic  zones  from  coinciding  with  the  physical  climatic 
zones. 

What  is  the  origin  of  winds? 

Name  the  currents  of  which  the  atmospheric  circulation 
principally  consists. 

Explain  the  action  of  the  rotation  of  the  earth  on  the 
direction  of  the  equatorial  and  polar  currents. 

Name  the  causes  which  produce  the  shifting  of  the  equa- 
torial and  polar  currents. 


100 


PHYSICAL    GEOGRAPHY. 


Name  the  principal  wind  zones  of  the  earth. 

Explain,  in  full,  the  origin  of  land  and  sea  breezes.  In 
what  respect  do  monsoons  resemble  land  and  sea  breezes  ? 

Name  the  principal  monsoon  regions  of  the  earth. 

Describe  the  origin  of  desert  winds? 

Name  the  winds  which  are  caused  by  the  desert  of  Sa- 
hara.   By  the  deserts  of  Arabia  and  Nubia. 

What  are  storms  ? 

What  are  cyclones?  Where  do  they  originate?  In 
what  direction  does  the  wind  rotate  in  the  northern 


hemisphere?  In  the  southern  hemisphere ?  In  what  di- 
rection does  the  storm  progress  in  each  hemisphere?  Ex- 
plain the  cause  of  the  rotation  of  the  wind. 

What  are  hurricanes?    Typhoons? 

Explain  the  formation  of  a  water-spout. 

Is  the  water  in  the  upper  part  of  a  water-spout  salt  or 
fresh  ? 

Name  the  important  facts  which  have  been  discovered 
respecting  the  north-easters  and  other  severe  storms  of  the 
United  States. 


MAP  QUESTIONS. 


-<k>>»4c 


Trace  on  the  map  of  isothermal  lines  the  areas  of  great- 
est heat  in  the  eastern  hemisphere.  In  the  western  hemi- 
sphere. 

Show  from  the  map  of  the  isothermal  lines  wherein 
the  physical  torrid  zone  differs  in  position  from  the 
mathematical  torrid  zone. 

In  which  hemisphere  do  the  isothermal  lines  deviate 
more  from  the  parallels  of  latitude,  in  the  northern  or 
the  southern? 

•  Trace  on  the  map  of  the  isothermal  lines  the  limit  of 
the  Arctic  drift  ice.    Of  the  Antarctic  drift  ice. 

What  are  the  mean  summer  and  winter  temperatures 
of  Sitka?    Of  Quebec? 

What  causes  exist  to  render  the  climate  of  Sitka  so 
much  warmer  than  that  of  Quebec,  notwithstanding  the 
difference  of  their  latitudes? 

What  are  the  mean  summer  and  winter  temperatures  of 
Mexico,  Madras,  Singapore,  Berlin,  London,  Philadelphia, 
Algiers,  Melbourne,  and  Eio  Janeiro? 

What  instances  can  you  find  on  the  map  of  the  in- 
crease in  the  mean  annual  temperature  of  places  through 


the  influence  of  ocean  currents?  Of  winds?  Of  rain- 
fall? 

Name  similar  instances  of  places  whose  mean  annual 
temperature  is  lowered  by  such  causes. 

Trace  on  the  map  of  the  winds  the  boundaries  of  the 
various  wind  zones.  State  the  direction  of  the  wind  in 
each  of  these  zones. 

Point  out  the  limits  of  the  monsoon  regions  of  the 
world. 

What  hot  winds  blow  over  Arabia?  Over  Egypt?  Over 
Greece  and  Italy  ?    Over  Guinea? 

What  cold  wind  blows  over  Texas? 

Describe  the  path  of  the  West  India  hurricanes.  How 
far  to  the  north  do  these  storms  extend  ? 

Describe  the  path  of  the  Mauritius  hurricanes.  Where 
do  these  storms  originate  ?  How  far  to  the  south  do  they 
extend  ? 

Describe  the  region  of  the  typhoons. 

Describe  the  route  a  vessel  would  take  in  sailing  from 
America  to  Europe.  From  New  York  to  San  Francisco, 
From  America  to  Australia. 


PRECIPITATION    OF    MOISTURE 


101 


Section  II. 


MOISTURE   OF  THE   ATMOSPHERE. 


->oXKc 


CHAPTER   I. 

Precipitation  of  Moisture. 

262.  Evaporation. — From  every  water  surface, 
and  even  from  masses  of  ice  and  snow,  there  is 
constantly  arising,  at  all  temperatures,  an  invisible 
vapor  of  water.  Water  vapor  is  about  three-fifths 
as  heavy  as  air.  It  diffuses  readily  through  the 
air,  and  is  borne  by  the  winds  to  all  parts  of  the 
earth.  This  giving  off  of  vapor  from  the  surface 
of  water  is  called  evaporation.  It  is  evaporation 
which  dries  the  wet  earth,  when  the  moisture  is 
unable  either  to  pass  off  the  earth's  surface  by 
drainage,  or  to  soak  through  the  porous  strata. 

About  one-half,  by  weight,  of  the  vapor  of  the  atmo- 
sphere is  within  a  little  over  a  mile  above  the  mean  sea 
level. 

263.  The  Rapidity  of  Evaporation  is  influ- 
enced by  the  following  circumstances: 

(1.)  The  temperature  of  the  atmosphere.  The 
capacity  of  the  air  for  absorbing  moisture  in- 
creases with  an  increase  of  temperature.  Warm 
air  can  retain  more  vapor  than  cold  air. 

(2.)  The  extent  of  surface  exposed.  Evapora- 
tion takes  place  only  from  the  surface ;  therefore, 
the  greater  the  surface,  the  greater  the  evapora- 
tion. 

(3.)  The  quantity  of  vapor  already  in  the  air. 
Dry  air  absorbs  moisture  more  rapidly  than  moist 
air.  All  evaporation  ceases  when  the  air  is  com- 
pletely saturated. 

(4.)  The  renewal  of  the  air.  During  very  calm 
weather,  the  air  in  contact  with  a  water  surface 
becomes  saturated,  and  so  prevents  further  evapo- 
ration. Gentle  breezes,  by  renewing  the  air,  in- 
crease the  rapidity  of  evaporation. 

(5.)  Pressure  on  the  surface.  A  diminished 
atmospheric  pressure  increases  the  rapidity  of 
evaporation. 

264.  The  Dew  Point. —  When  the  air  contains 
as  much  vapor  as  it  is  capable  of  holding,  it  is 
said  to  be  at  its  dew  point. 

The  quantity  of  moisture  necessary  to  saturate  a  given 
quantity  of  air  and  bring  it  to  the  dew  point,  varies  with 


the  temperature.  Cold  air  requires  less  moisture  to  satu- 
rate it  than  air  which  is  warmer,  and,  therefore,  may  feel 
damper  than  warm  air,  which  may  contain  more  vapor. 
We  thus  distinguish  between  the  actual  humidity,  or  the 
amount  actually  present  in  a  given  volume  of  air,  and 
the  relative  humidity,  or  the  relation  between  the  amount 
present  and  that  required  to  saturate  the  air  at  the  given 
temperature. 

The  humidity  of  the  air  is  determined  by  means  of  an 
instrument  called  a  hygrometer. 

Weight  in  grains  of  aqueous  vapor  in  one  cubic  foot  of 
satubated  AIR  at  different  temperatures.     (Silliman.) 


Temperature,  Fahr. 

Weight  in  Grains. 

Approximate  Values. 

0°  « 

0.545 

0.6 

10° 

0.841 

0.9 

20° 

1.298 

1.3 

7*  30° 

1.969 

2.0 

40° 

2.862 

2.9 

50° 

4.089 

4.1 

60° 

5.756 

5.8 

70° 

7.992 

8.0 

80° 

10.949 

11.0 

.    90° 

14.810 

15.0 

100° 

19.790 

20.0 

No  matter  how  much  aqueous  vapor  a  given 
quantity  of  air  contains,  if  its  temperature  be 
lowered,  it  will  grow  relatively  moister  until,  if  the 
fall  of  temperature  be  sufficient,  its  dew  point  is 
reached;  and  as  soon  as  the  temperature  falls 
below  the  dew  point,  a  deposition  of  moisture 
will  begin,  either  in  the  liquid  or  solid  state. 

265.  Precipitations. — The  invisible  vapor  may 
be  precipitated  from  the  atmosphere  and  become 
visible,  either  as  dew,  mist,  fog,  cloud,  rain,  sleet, 
hail,  or  snow.     These  are  called  precipitations. 

Law  of  Precipitations. 

In  order  that  any  precipitation  may  occur,  the 
air  must  be  cooled  below  the  temperature  of  its'  dew 
point. 

266.  Distribution  of  Precipitations. — The  quan- 
tity of  moisture  in  the  air  depends  on  its  tempera- 
ture, and  its  vicinity  to  the  sea. 

The  amount  of  precipitation  regularly  decreases 
as  we  pass  from  the  equator  to  the  poles,  and  from 
the  coasts  of  the  continents  toward  the  interior. 

267.  Dew. — If,  during  a  warm  day,  a  dry  glass 
be  filled  with  cold  water,  the  outside  of  the  glass 
will  soon  become  covered  with  small  drops  of 
water,  derived  entirely  from  the  air.     The  air 


102 


PHYSICAL    GEOGRAPHY. 


which  comes  in  contact  with  the  cool  sides  of  the 
glass  has  its  temperature  lowered  below  the  dew 
point,  and  deposits  as  vapor  the  moisture  it  no 
longer  can  retain. 

The  dew  which  is  deposited  during  certain  sea- 
sons of  the  year  on  plants  and  other  objects  on 
the  earth,  has  a  similar  origin.  Objects  on  the 
earth  cool  more  rapidly  than  the  surrounding  air, 
which  deposits  its  moisture  on  them  whenever 
they  lower  its  temperature  below  the  dew  point. 
When  the  objects  are  colder  than  32°  Fahr.,  the 
dew  is  deposited  as  hoar-frost. 

Dew  falls  more  heavily  on  some  objects  than 
on  others ;  this  is  because  some  objects  radiate  or 
give  off  their  heat  more  rapidly  than  others,  and 
thus  becoming  cooler,  they  condense  more  of  the 
moisture  of  the  air. 

More  dew  falls  during  a  clear  night  than  during 
a  cloudy  one,  because  objects  cool  more  rapidly 
when  the  sky  is  clear  than  when  it  is  cloudy. 

Thick  clothing  keeps  the  body  warm,  not  because  the 
clothes  give  any  heat  to  the  body,  but  because  they  are  non- 
conductors, and  prevent  the  escape  of  heat  from  the  body. 
In  like  manner  the  clouds,  acting  as  blankets  to  the  earth, 
prevent  its  losing  heat  rapidly. 

More  dew  falls  during  a  still  night  than  during 
a  vrindy  one. 

The  air  must  remain  long  enough  in  contact 
with  cold  objects  to  enable  them  to  lower  its  tem- 
perature and  collect  its  moisture.  Powerful  winds 
prevent  this,  while  gentle  breezes  favor  the  depo- 
sition, by  bringing  fresh  masses  of  air  into  contact 
with  the  cold  objects. 

In  the  tropics,  during  seasons  when  the  sky  is  clear,  the 
dew  is  so  copious  that  it  resembles  a  gentle  rain. 

In  the  deposition  of  dew,  the  moisture  is  derived  from  a 
comparatively  thin  stratum  of  air  in  the  immediate  neigh- 
borhood of  the  cool  object.  All  other  kinds  of  precipita- 
tions are  produced  by  the  cooling  of  a  large  mass  of  air. 

268.  Fogs  and  Clouds. — Whenever  the  tem- 
perature of  a  large  mass  of  air  is  reduced  below 
its  dew  point,  its  moisture  begins  to  collect  in 
minute  drops,  which  diminish  the  transparency 
of  the  air,  and  form  fogs  or  mists,  when  near  the 
surface,  and  clouds,  when  in  the  upper  regions  of 
the  atmosphere.  Fogs  and  clouds  are  the  same  in 
their  origin  and  composition,  and  differ  only  in 
their  elevation. 

The  minute  drops  of  water  that  form  clouds 
and  fogs,  though  formed  of  a  substance  about 
eight  hundred  times  heavier  than  air,  are  pre- 
vented from  settling  rapidly  by  the  resistance  of 
the  air.     This  is  rendered  possible  by  the  minute 


size  of  the  drops,  which  are  much  smaller  than 
the  relatively  heavier  dust-particles,  which  are 
wafted  about  by  the  winds.  Whenever  the  drops 
exceed  a  certain  size,  they  fall  as  rain  or  snow. 

It  was  once  believed  that  the  moisture  in  fogs  and  clouds 
existed  in  the  form  of  hollow  bubbles  or  vesicles,  filled 
with  air,  and  that  the  clouds  or  fogs  ascended,  whenever 
the  contained  air  expanded  the  bubbles  and  rendered 
them  specifically  lighter.  This  idea  is  now  generally 
abandoned. 

Clouds  or  fogs  result  whenever  a  mass  of  air  is 
cooled  below  the  temperature  of  its  dew  point, 
as,  for  example,  when  two  bodies  of  air  of  dif- 
ferent temperatures  are  mingled,  especially  if, 
as  is  generally  the  case,  the  warmer  of  the  two 
is  the  moister.  On  the  contrary,  clouds  or  fogs 
disappear  on  the  approach  of  a  dry,  warm  wind. 
Clouds  are  higher  in  the  tropics  than  in  the  polar 
regions,  and  generally  are  higher  during  the  day 
than  during  the  night. 

Off  the  banks  of  Newfoundland,  the  warm,  moist  air  of 
the  Gulf  Stream  is  cooled  by  the  cold,  moist  air  of  the 
Labrador  ocean  current.  Hence  result  the  dense  fogs  so 
frequent  over  this  part  of  the  ocean. 

269.  Classification  of  Clouds. — Clouds  assume 
such  a  variety  of  shapes,  that  it  is  difficult  to 
classify  them.  Meteorologists,  however,  have  rec- 
ognized the  existence  of  four  primary  forms :  the 
cirrus,  the  cumulus,  the  stratus,  and  the  nimbus. 


Fig.  90.    Primary  Forms  of  Clouds. 
■v  Cirrus,  -v  -v-  Cumulus. 

The  Cirrus  Cloud  consists  of  fleecy,  feathery 
masses  of  condensed  vapor,  deposited  in  the 
higher  regions  of  the  atmosphere.  The  name 
cirrus  is  derived  from  the  resemblance  the  cloud 
bears  to  a  lock  of  hair.     These  clouds  are  called 


PRECIPITATION    OF    MOISTURE. 


103 


by  sailors  cats'  tails  or  mares'  tails.  From  their 
elevation,  the  moisture  is,  probably,  generally  in 
the  condition  of  ice-particles.  Halos,  or  circular 
bands  of  light  around  the  sun,  are  caused  by  light 
passing  through  cirrus  clouds. 

The  Cumulus,  or  Heap  Cloud,  is  a  denser  cloud 
than  the  cirrus,  and  is  formed  in  the  lower  re- 
gions of  the  air,  where  the  quantity  of  vapor  is 
greater.  Cumulus  clouds  generally  consist  of 
rounded  masses,  in  the  shape  of  irregular  heaps, 
with  moderately  flat  bases.  They  are  caused  by 
ascending  currents  of  air,  which  have  their  moist- 
ure condensed  by  the  cold  produced  by  expan- 
sion and  elevation.  Cumulus  clouds  occur  dur- 
ing the  hottest  part  of  the  day.  Their  height 
seldom  exceeds  two  miles. 


Fig,  91.    Primary  Forms  of  Clouds. 
■v  Nimbus,   -v  -v  Stratus. 

The  Nimbus,  or  Storm  Cloud,  is  any  cloud  from 
which  rain  falls.  Any  of  the  various  forms  of 
clouds  may  collect  and  form  a  nimbus  cloud. 
The  nimbus  is  not  considered  as  a  distinct  form 
of  cloud  by  some  meteorologists. 

The  Stratus,  or  Layer  Clouds,  form  in  long, 
horizontal  sheets  or  bands.  These  clouds  are 
most  common  in  the  early  morning  and  evening, 
when  the  ascending  currents  are  weak.  They 
are  caused  by  the  gradual  settling  of  cumulus 
and  other  clouds.  The  stratus  is  the  lowest  form 
of  cloud ;  it  sometimes  falls  to  the  surface  of  the 
earth,  and  becomes  a  fog. 

The  cirrus,  stratus,  and  cumulus  clouds  assume 
a  variety  of  shapes,  producing  various  secondary 
forms. 

270.  Secondary  Forms  of  Clouds. — The  cirro- 
stratus,  the  cirro-cumulus,  and  the  cumulo-stratus 


are  the  most  prominent  secondary  forms  of 
clouds.  The  first  two  are  modifications  of  the 
cirrus  cloud ;  the  latter,  of  the  cumulus. 


Fig,  92.    Secondary  Forms  of  Clouds. 
•v-Cirro-Cumulus.  -v  -vCirro-Stratus.  -v--v-*-Cumulo-Stratus. 

The  Cirro-Cumulus  is  a  cirrus  cloud,  arranged 
in  little  rounded  masses,  shaped  something  like 
cumuli.  They  are  sometimes  called  "  wool  sacks," 
and  indicate  dry  weather. 

The  Cirro-Stratus  is  a  cirrus  cloud  which  has 
settled  in  bands  or  layers.  The  bands  are  not 
continuous,  but  are  arranged  in  blotches  or  bars, 
and  often  give  to  the  sky  the  speckled  appear- 
ance of  a  mackerel's  back,  producing  the  so-called 
mackerel  sky. 

The  appearance  of  a  mackerel  sky  indicates — 1.  That 
the  moisture  of  the  upper  strata  of  air  is  condensing;  2. 
That  it  is  growing  dense  enough  to  arrange  itself  in 
layers.  Therefore,  a  mackerel  sky  generally  indicates 
approaching  rain. 

The  Cumulo-Stratus  is  the  form  produced  by 
the  heaping  together  of  a  mountain-like  mass  of 
cumulus  clouds ;  the  base  partakes  of  the  nature 
of  the  stratus  cloud,  but  the  top  clearly  resembles 
cumuli.  These  clouds  differ  but  little  from  the 
nimbus,  or  storm  cloud. 

271.  Rain. — When,  during  the  formation  of  a 
cloud,  the  condensation  of  moisture  continues,  the 
drops  of  which  the  cloud  is  composed  increase 
in  size,  and,  uniting,  fall  to  the  earth  as  rain. 
Rain  which  freezes  while  falling  forms  sleet.    As 


104 


PHYSICAL    GEOGRAPHY. 


the  drops  fall  through  the  cloud  they  grow  larger 
by  the  addition  of  other  drops  which  unite  with 
them.  Raindrops,  therefore,  are  larger  when  the 
clouds  are  thicker.  They  are,  in  general,  larger 
in  the  tropics  than  in  the  polar  regions,  and  dur- 
ing the  day  than  at  ni^ht. 

To  produce  rain,  it  is  necessary  that  the  tem- 
perature of  a  large  mass  of  air  be  reduced  con- 
siderably below  its  dew  point  There  are  several 
ways  in  which  this  cooling  may  be  effected : 

(1.)  By  a  change  of  latitude.  A  warm,  moist- 
ure-laden wind  may  blow  into  a  cold  region.  The 
equatorial  currents  of  air  deposit  their  moisture 
in  the  temperate  and  polar  zones  on  account  of 
the  chilling  experienced  as  they  recede  from  the 
equator. 

(2.)  By  a  change  of  altitude.  By  an  ascending 
current  of  air,  which  carries  the  moisture  of  the 
lower  strata  into  the  upper  regions,  where  the 
cold  there  existing,  together  with  that  produced 
by  the  rapid  expansion  of  both  air  and  vapor 
under  the  diminished  pressure,  condenses  the  moist- 
ure of  the  air.  It  is  mainly  in  this  manner  that 
the  rains  of  the  tropical  regions  are  caused. 

The  rain  in  mountainous  districts  has  a  similar 
cause.  A  moist  wind,  reaching  a  mountain-range, 
is  forced  by  the  wind  back  of  it  to  ascend  the 
slopes.  Contact  with  the  cold,  upper  slopes  causes 
condensation  of  the  vapor  as  rain. 

(3.)  The  mingling  of  masses  of  cold  and  warm 
air.  By  this  means  heavy  clouds  and  a  moderate 
rainfall  may  be  produced ;  but  the  precipitation 
can  never  be  considerable,  because  the  cooler  air 
will  be  warmed  by  the  mixing,  and,  therefore, 
will  have  its  capacity  for  moisture  increased  in- 
stead of  diminished. 

272.  Distribution  of  the  Rainfall.— The  dis- 
tribution of  rain  may  be  considered  both  as  re- 
gards its  periodicity  and  its  quantity.  The  distri- 
bution of  the  rain  is  dependent  upon  the  direction 
of  the  winds.  Each  wind  zone  has  a  character- 
istic rainfall. 

The  following  simple  principles  determine  the 
rainfall  in  any  particular  wind  zone: 

(1.)  The  equatorial  currents  are  rain-bearing, 
because  they  are  moist,  and  while  on  their  way 
to  the  poles,  their  temperature  and  consequent 
capacity  for  moisture,  is  constantly  decreasing. 

(2.)  The  polar  currents  are  dry,  because  they 
are  constantly  increasing  in  temperature  as  they 
approach  the  equator ;  hence  they  take  in,  rather 
than  give  out,  moisture. 


When  they  have  reached  the  zones  of  the  trade  winds, 
the  polar  currents  may  bring  abundant  rains,  provided 
they  have  previously  crossed  an  ocean.  They  then  dis- 
charge the  moisture  with  which  they  are  saturated,  either 
by  an  ascending  current,  or  by  blowing  against  the  ele- 
vations of  the  continent. 

273.  Periodical  Rain  Zones. 

The  Zone  of  Calms. — In  the  zone  of  calms  it 
rains  nearly  every  day.  In  the  early  morning 
the  sky  is  cloudless ;  but  near  the  middle  of  the 
day,  as  the  heat  increases,  the  ascending  currents, 
rising  higher,  begin  to  condense  their  moisture; 
cumuli  clouds  form,  and,  increasing  rapidly,  soon 
cover  the  sky,  when  torrents  of  rain  descend,  ac- 
companied by  thunder  and  lightning.  After  a 
few  hours  the  rain  ceases,  and  the  sky  again  be- 
comes clear.  In  this  zone  it  seldom  rains  at 
night. 

274.  The  Zone  of  the  Trades. — Since  the  trades 
are  generally  dry  winds,  it  is  only  when  their  tem- 
perature is  considerably  decreased  that  they  can 
cause  rain.  In  the  zone  of  the  trades,  except  in 
mountainous  districts  and  on  the  windward  coasts 
of  a  continent,  the  rainfall  occurs  during  the 
greatest  heat  of  the  season,  when  the  sun  is  di- 
rectly overhead  and  the  ascending  currents  are 
powerful.  Hence,  it  rains  during  a  few  months 
in  summer,  when  immense  quantities  of  water 
fall ;  the  remainder  of  the  year  is  dry.  Copious 
dews,  however,  occur  at  night. 

The  precipitation  is  not  continuous  throughout  the  en- 
tire summer.  Since  the  rain  only  falls  when  the  sun  is 
nearly  overhead,  a  brief  interval  of  dry  weather  occurs 
in  regions  near  the  equator,  thus  dividing  the  season  into 
two  parts :  one,  during  the  passage  of  the  sun  over  the 
zenith;  the  other,  on  his  return  to  the  zenith  from  the 
adjacent  tropic.  Near  the  limits  of  the  zone,  however,  the 
two  seasons  are  merged  into  one. 

Over  the  ocean,  during  most  of  the  year,  there 
is  no  rain  in  the  zone  of  the  trades,  although  the 
actual  humidity  of  the  .air  is  quite  high. 

Between  latitude  24°  and  30°,  in  both  the  Northern  and 
Southern  Hemispheres,  there  are  regions  of  comparatively 
scanty  rains.  Here  the  summers  are  not  hot  enough  to 
cause  rain  by  the  ascending  currents,  but  are  sufficiently 
hot  to  prevent  the  equatorial  current  from  bringing  much 
rain.  Here  also  the  return  branch  of  the  equatorial  cur- 
rent becomes  drier  on  its  return  to  the  equator. 

275.  The  Monsoon  Region  of  the  Indian  Ocean. — 
During  the  prevalence  of  the  winter  monsoon,  the  north- 
east winds  bathe  the  eastern  shores  of  Hindostan  in  copious 
rains,  while  the  western  shores,  shielded  by  the  ranges  of 
the  Ghauts,  are  dry.  During  the  summer  monsoon,  the 
south-west  winds  bathe  the  western  shores  and  the  south- 
ern slopes  of  the  Himalayas  in  heavy  rains,  while  the 
eastern  shores  are  dry.  This  monsoon  also  brings  rains  to 
the  western  coasts  of  the  peninsula  of  Indo-China. 


PRECIPITATION    OF    MOISTURE. 


105 


276.  Non-Periodical  Rain  Zones. 

The  Zones  of  the  Variable  Winds. — In  these 
zones  rain  may  occur  at  any  season  of  the  year, 
and  at  any  hour  of  the  day  or  night.  Here  it 
is  the  equatorial  currents  which  bring  the  rain. 
These  regions  are  sometimes  called  the  zones  of 
perennial  rains,  or  of  constant  precipitation.  In 
the  greater  part  of  these  zones,  the  equatorial 
currents  are  more  frequent  in  summer  than  in 
winter.  The  rainfall  is,  therefore,  greatest  dur- 
ing summer. 

Rainfall  in  the  Zone  of  the  Polar  Winds. — In 
these  zones  the  winters  are  dry,  because  the  dry, 
cold  polar  currents  then  prevail ;  but  during  the 
summer  the  equatorial  currents  sometimes  pre- 
vail, and  bring  with  them  dense  clouds  and  fogs, 
accompanied  by  drizzling  rains.  The  snows  occur 
mainly  in  spring  and  autumn. 

277.  Quantity  of  Rain. — The  quantity  of  rain 
which  falls  in  a  given  time  on  any  area  is  deter- 
mined by  means  of  an  instrument  called  the  rain- 
gauge  or  pluviometer. 

The  rain-gauge  is  generally  constructed  in  the  form  of 
a  cylindrical  vessel  with  a  horizontal  base,  surmounted 
by  a  funnel-shaped  top.  A  vertical  glass  tube  communi- 
cates with  the  bottom  of  the  vessel  from  the  outside, 
and  allows  the  water  to  mount  in  it  to  the  same  height 
as  that  in  the  inside.  The  rain-gauge  is  placed  in  an  ex- 
posed position,  where  it  is  free  from  eddies  or  whirls. 
If,  during  any  given  time,  the  water  in  the  instrument 
is  one  inch  deep,  then  during  that  time  the  rainfall  over 
the  area  equals  one  inch.  In  speaking  of  the  rainfall  of 
a  country,  the  moisture  which  may  fall  as  snow  is  always 
included. 

An  inch  of  rain  over  a  surface  a  square  yard 
in  area  equals  in  weight  46!  pounds :  on  the  sur- 
face of  an  acre,  it  is  nearly  equal  in  weight  to 
100  tons. 

The  annual  rainfall  is  distributed,  as  regards 
quantity,  as  follows : 

Irrespective  of  the  elevations  of  the  surface, 
more  rain  falls  in  the  tropics  than  in  the  temperate 
regions,  and  more  in  the  temperate  than  in  the 
polar  regions.  The  quantity  thus  decreases  with 
moderate  regularity  from  the  equator  toward  the 


poles.    This  is  caused  by  a  similar  decrease  in  the 
quantities  of  heat  and  evaporation. 

While  the  amount  of  rain  that  falls  decreases  from  the 
equator  to  the  poles,  the  number  of  cloudy  or  rainy  days 
increases,  being  greater  at  the  poles  than  at  the  equate , 

More  rain  falls  on  the  coasts  of  a  continent  than 
in  the  interior,  since  near  the  ocean  the  winds  are 
moister.  That  coast  of  a  continent  which  first 
receives  the  prevailing  wind  has  the  greatest 
rainfall. 

More  rain  falls  in  the  Northern  Hemisphere  than 
in  the  Southern.  This  is  due  to  the  greater  extent 
of  the  land-area  of  the  Northern  Hemisphere. 

Mountains  receive  a  heavier  rainfall  than  the 
plains  below,  because  the  moist  winds,  in  order 
to  cross  the  mountains,  are  forced  to  ascend  their 
slopes  and  thus  pass  into  a  colder  region  of  the 
atmosphere*.  Therefore,  the  sources  of  rivers  are 
generally  found  in  mountainous  districts.  Moun- 
tains are  among  the  most  important  causes  of  rain. 

When  the  mountains  are  high,  the  winds  may 
reach  the  opposite  slopes  dry  and  vaporless.  The 
tropical  Andes  of  South  America  afford  an  excel- 
lent example  of  this. 

Plateaus,  though  higher  than  plains,  receive,  as 
a  rule,  less  rain,  because  they  are  generally  sur- 
rounded by  mountain  chains,  which  rob  the  winds 
of  their  moisture.  Moreover,  the  air  over  a  pla- 
teau is  warmer  than  at  a  corresponding  height  in 
the  atmosphere,  and  therefore  dissolves,  rather 
than  condenses,  the  moisture. 

The  rainfall  of  the  New  World,  both  in  the 
tropical  and  temperate  regions,  is  greater  than 
that  of  the  Old ;  thus,  in  the  tropics  of  the  New 
World,  115  inches  of  rain  fall  yearly,  while  the 
same  portions  of  the  Old  World  receive  but  77 
inches.  In  the  temperate  zones  in  America  the 
annual  rainfall  is  39  inches,  while  in  Europe  it 
is  but  34  inches. 

The  mean  annual  rainfall  at  Philadelphia,  according  to 
Prof.  Kirkpatrick,  is  46.93  inches.  The  figures  are  based 
on  observations  during  16  consecutive  years. 

The  preceding  principles  find  ample  illustration  in  the 
following  tables : 


Table  of  Annual  Eainfall  (H.  K.  Johnston). 
Rainfall  in  the  Tropics. 


OLD  WOELD. 

Inches. 

Ceylon 91.7 

Hindostan,  mean  of  the  Peninsula 117.5 

Sierra  Leone,  Guinea 189.6 

Macao,  China 68.3 

Canton 69.2 


NEW  WOELD. 

Inches. 

San  Luis  de  Maranhao,  Brazil 280.00 

Cayenne,  Guiana 116.27 

Paramaribo,  Guiana 229.20 

Grenada,  Lesser  Antilles 103.41 

Havana,  Cuba 90.66 


106 


PHYSICAL    GEOGRAPHY. 


Rainfall  in  the  Temperate  Zone. 


Inches. 

Madeira 29.82 

Sicily 23.55 

W.  side  of  Apennines.. 35. 17 
E.  "  "  ..26.70 

S.  "    Alps 57.57 

N.  "        "   35.27 


Inches. 

Southern  France 23.54 

Southern  Germany 26.64 

Netherlands 26.70 

British  Islands,  Plain..27.00 

"  "        Mts.... 50.00 

W.  Coast  Scandinavia..82.12 


Mean  Eainfall   in  Europe  in  the  Temperate 
Zone 34  inches. 


AMERICA. 

Inches. 

Key  West,  Florida 35.26 

Charleston,  S.  C 47.60 

Washington,  D.  C 36.30 

Marietta,  Ohio 34.16 

West  Chester,  Penna 46.89 

Cambridge,  Mass 38.42 

Burlington,  Vt 39.44 

Eastport,  Maine 36.28 

New  York 36.28 

Mean  Eainfall  in  the  United  States  in  the 
Temperate  Zone 39  inches. 


610  ins. 


600  ins. 
500  " 
400  " 
300  " 
200  " 
100  " 


301  ins. 


167  ins. 


107.6  ins. 


82  ins. 


46.9  ins. 


ins.   32  ins. 


Cherrapon-    Mahabulesh-    Vera  St.  Do-       Bergen,      Philadelphia,    Cambridge,      British        Alexandria, 

gi,  India.       war,  India.      Cruz.  mingo.       Norway.  Penna.  Mass.  Isles.  Egypt. 

Fig,  93.    Comparative  Rainfall.     (The  figures  represent  the  annual  rainfall  in  inches.) 


278.  Rainless  Districts. — In  some  parts  of  the 
world,  rain  is  either  entirely  absent,  or  falls  only 
in  limited  quantities,  at  long  intervals.  The  most 
extensive  rainless  districts  are  found  in  the  east- 
ern continent. 

Desert  Belt  of  the  Eastern  Continent. — From 
the  western  shores  of  Northern  Africa  eastward 
to  the  Great  Kinghan  Mountains  in  Asia,  extends 
an  almost  uninterrupted  belt  of  desert  lands.  It 
includes  the  great  desert  of  the  Sahara,  the  Ara- 
bian and  Persian  Deserts,  and  the  Desert  of  Mon- 
golia. The  aridity  is  most  absolute  in  the  west, 
where,  in  the  Sahara  and  in  the  desert  of  Arabia, 
rain  seldom,  if  ever,  falls.  Toward  the  east,  in 
Persia  and  Mongolia,  scanty  rains  occur,  but  the 
country  has  the  appearance  of  a  desert. 

The  cause  of  this  immense  desert  tract  is  to  be 
found  in  the  dry  trade  winds,  which  blow  over 
most  of  the  region.  Having  previously  crossed 
the  vast  continent  of  Asia  as  upper  currents,  they 
arrive  at  the  deserts  dry  and  vaporless.  Even 
that  portion  of  the  region  which  receives  the 
winds  from  the  Mediterranean  has  no  rainfall, 
because  any  clouds  that  may  form,  are  soon  dis- 
sipated by  the  hot  air  of  the  desert. 

Persia  and  Mongolia  owe  their  deserts  to  their 


high  mountain  borders,  which  rob  the  clouds  of 
their  moisture  before  they  cross  the  interior  pla- 
teaus. The  high  system  of  the  Himalayas  effect- 
ually prevents  any  of  the  moisture  of  the  south- 
west currents  from  penetrating  the  plateau  of 
Mongolia. 

Arid  tracts  occur  in  the  Kalahari  desert,  in  Africa,  and 
near  the  tropic  of  Capricorn,  in  Australia. 

Desert  Belt  of  the  Western  Continent. — The 
desert  lands  of  the  Western  Continent  are  more 
contracted  in  area.  In  North  America,  the  largest 
desert  is  in  the  Great  Interior  Plateau.  Here  the 
mountain  borders,  especially  the  Sierra  Nevada 
on  the  west,  deprive  the  interior  of  rain.  The 
aridity  is  not  absolute,  since  scanty  rains  occur 
over  parts  of  the  region.  Portions  of  the  penin- 
sula of  California  and  of  the  Mexican  Plateau 
also  resemble  deserts. 

In  South  America,  on  the  western  slopes  of  the 
Andes,  between  the  parallels  of  27°  and  23°  S., 
is  found  the  desert  of  Atacama.  Here  rain  never 
falls,  although  the  ground  is  occasionally  refreshed 
by  mists  and  dews.  The  cause  of  the  absence  of 
rain  is  to  be  traced  to  the  high  Andes,  which  con- 
dense all  the  moisture  of  the  trades  on  their  east- 


HAIL,    SNOW,    AND    GLACIERS. 


107 


em  slopes,  the  winds  thus  arriving  dry  and  va- 
porless  at  the  western. 

Cause  of  Deserts. — Deserts  are  caused  entirely 
by  the  absence  of  moisture.  Their  soil,  though  gen- 
erally finely  pulverized,  or  sand-like,  does  not  dif- 
fer, save  in  the  absence  of  vegetable  mould,  from 
that  of  other  areas.  Thus  neither  the  nature  of 
its  temperature,  nor  its  soil,  is  the  cause  of  the 
desert  of  Sahara,  since  a  vigorous  vegetation  al- 
ways follows  the  appearance  of  Avater,  on  the  suc- 
cessful boring  of  an  artesian  well.  It  is  probably 
true  that  deserts,  once  formed,  tend  to  perpetuate 
themselves,  by  the  influence  their  naked  surfaces 
exert  on  the  rainfall. 


>*k° 


CHAPTER  II. 
Hail,  Snow,  and  Glaciers. 

279.  Hail  falls  when  considerable  differences 
of  temperature  exist  between  higher  and  lower 
strata  of  air,  and  the  moisture  is  suddenly  con- 
densed in  the  presence  of  great  cold.  Generally, 
several  layers  or  bands  of  dark,  grayish  clouds 
are  seen.  Hail  falls  most  frequently  in  summer, 
near  the  close  of  an  excessively  warm  day. 

Structure  of  the  Hailstone. — If  a  large  hailstone  be 
placed  on  a  hot  surface  until  one-half  is  melted,  the  struc- 
ture can  be  readily  examined.  Concentric  layers,  similar 
to  those  of  an  onion,  will  be  noticed,  arranged  around  a 
central  nucleus,  sometimes  of  ice  and  sometimes  of  snow, 
though  generally  the  latter.  The  stones  are  more  or  less 
oblately  spheroidal  in  shape.  Their  general  weight  varies 
from  a  few  grains  to  several  ounces,  but  they  have  been 
known  to  weigh  several  pounds. 


Fig.  94.    Structure  of  a  Hailstone. 

Origin  of  Hail.— The  cause  of  hail  is  not  ex- 
actly understood,  and  several  theories  have  been 
framed  to  account  for  it.  One  of  these  is  the 
Rotary  Theory. 

The  wind  i3  supposed  to  rotate  as  in  a  cyclone,  only  the 
axis  of  the  whirl  is  horizontal  instead  of  vertical.  Two 
horizontal  layers  of  cloud  exist— the  upper  layer  of  snow, 
the  lower,  of  rain.  The  snowflakes,  which  form  the  nu- 
clei of  the  hailstones,  are  caught  in  the  whirl,  and  dipped 
13 


in  rapid  succession  into  the  two  clouds,  thus  receiving  al- 
ternate coatings  of  ice  and  snow,  until  at  last  they  are 
hurled  to  the  ground. 


Fig.  95.    Kotary  Theory  of  Hail. 

Thunder  and  lightning  are  the  invariable  attendants  of 
hailstorms,  and  some  authorities  have  attributed  the  for- 
mation of  the  stones  to  successive  electrical  attractions 
and  repulsions  of  the  snowflakes  between  a  snow  and  a 
rain  cloud.  Others  have  imagined  a  number  of  alternate 
layers  of  snow  and  rain,  and  have  attributed  the  hail- 
stones to  drops  of  rain  falling  through  the  successive 
clouds. 

280.  Snow. — When  the  moisture  of  the  air  is 
condensed  at  any  temperature  below  32°  Fahr., 
the  vapor  crystallizes,  and  snowflakes  are  formed. 

The  snowflakes  grow,  as  they  fall,  by  condensing  addi- 
tional moisture  from  the  air.  They  are  larger  in  mild 
than  in  cold  weather. 

Snow-crystals  assume  quite  a  variety  of  forms,  but  are 
built  up  by  various  groupings  of  minute  rhombohedrons 
of  ice.    The  star-shape  is  the  most  common. 


Fig.  96.    Snow-Crystals. 

If  the  temperature  of  the  air  near  the  surface 
is  much  warmer  than  32°  Fahr.,  any  snow  that 
is  formed  in  the  upper  regions  will  melt  before 
reaching  the  ground.  Hence,  in  the  temperate 
zones,  as  a  rule,  snow  falls  only  in  winter,  while 
in  the  tropics  it  never  falls,  except  near  the  sum- 
mits of  lofty  mountains. 

It  is  a  mistake  to  suppose  that  the  fall  of  snow  is  greater 
in  regions  near  the  poles  than  elsewhere ;  for  in  high  lati- 


108 


PHYSICAL    GEOGRAPHY. 


tudes  there  is  comparatively  little  moisture  in  the  air. 
The  fall  is  heaviest  in  the  cool  temperate  regions. 

281.  Snow  Line. — The  snow  which  falls  on 
mountains  is  slowly  pressed  down  the  slopes  by 
the  weight  of  the  snow  above.  The  distance  it 
will  move  down  the  mountain  before  melting  de- 
pends on  a  number  of  circumstances.  The  lower 
limit  of  the  line,  above  which  the  ground  remains 
covered  with  snow  throughout  the  year,  is  called 
the  snow  line. 

The  height  of  the  snow  line  depends — 

(1.)  On  the  amount  of  the  snowfall.  The  greater 
the  fad,  the  farther  down  the  mountain  the  snow 
will  move  before  melting. 

(2.)  On  the  temperature  of  the  valley.  The 
warmer  the  valley  the  higher  the  snow  line. 
The  snow  line  is,  therefore,  highest  in  the  trop- 
ical regions,  and  lowest  near  the  poles. 

(3.)  On  the  inclination  of  the  mountain  slope. 
The  steeper  the  slope,  the  more  rapidly  the  snow 
will  move  down  the  mountain,  and  the  farther  it 
will  go  before  melting,  therefore,  the  lower  the 
snow  line. 

According  to  Guyot,  the  snow  line,  subject  to  variations, 
is  about  three  miles  above  the  sea  in  the  tropics ;  rather 
less  than  two  miles  in  the  temperate  latitudes ;  and  less 
than  a  mile  near  the  northern  extremities  of  the  conti- 
nents ;  while  still  farther  north,  on  the  polar  islands,  the 
snow  line  is  but  a  few  hundred  feet  above  the  sea.  Over 
the  polar  oceans,  the  winter  snows  are  but  partially  melted, 
and  help  to  produce  the  huge  ice-floes  of  these  regions. 

SNOW   LINE. 

Europe.— Norway,  lat.  70°  N 3,400  feet. 

"  "    60°  N 5,500  " 

"  Alps,  lat.  46°  N.  (south  side) 9,200  " 

"        "       (north  side) 8,800  " 

Asia.— Altai  Mountains,  lat.  50°  N 7,000  " 

"       Himalayas,  lat.  31°  N 17,000  " 

Africa.— Kiliinandjaro,  lat.  3°  S 16,000  " 

North  America. — Rocky   Mountains,   lat. 

43°  N 12,467  " 

South  America. — Andes,  Ecuador,  lat.  1°  S.  15,800  " 

lat.  54°  S 3,700  " 

The  snow  line  is  generally  lower  in  a  moist  atmosphere 
than  in  dry  air,  because  of  the  greater  fall  of  snow  in  the 
former  case  than  in  the  latter.  As  a  rule,  that  slope  of  a 
range  which  is  exposed  to  the  prevalent  wind  has  a  lower  snow 
line  than  the  opposite  slope.  The  position  the  slope  occupies 
in  relation  to  the  vertical  rays  of  the  sun,  also  exerts  an 
influence  on  the  height  of  the  snow  line. 

282  Glaciers  are  immense  masses  of  ice  and 
snow,  which  move  almost  imperceptibly  down  the 
higher  mountain  valleys  or  slopes.  Their  upper 
parts  are  formed  of  soft  snow ;  their  lower  por- 
tions of  clear,  hard  ice.  Their  origin  is  as  fol- 
lows :  The  weight  of  the  huge  snow  fields,  which 


form  above  the  snow  line,  presses  the  mass  slowly 
down  the  slopes.  The  pressure,  due  to  the  weight 
of  the  layers,  but  especially  the  pressure  which  is 
produced  when  the  mass  is  forced  through  a  con- 
traction in  the  valley,  squeezes  out  the  confined 
air,  to  which  snow,  in  great  part,  owes  its  white 
color,  and  the  lower  part  of  the  glacier  thus  be- 
comes changed  into  a  compact  mass  of  pure  ice. 
The  alternate  thawing  and  freezing  to  which  the 
mass  is  subjected  below  the  snow  line,  also  con- 
tribute to  the  change  from  snow  to  ice. 

The  change  is  most  thorough  in  the  lower  parts  of  the 
glacier,  where  the  ice  is  marvellously  clear.  Its  color, 
when  seen  in  great  depths,  is  of  a  deep  azure  blue ;  in  the 
middle  portions  of  the  glacier  the  ice  is  coarse  and  white. 
The  higher  region  of  but  partially  changed  snow  is  called 
the  neve  region.  Here  the  snow  occurs  in  coarse  white 
grains.  The  process  of  formation  is  a  continuous  one. 
The  neve  region  is  supplied  by  fresh  falls  of  snow,  which 
replace  those  pressed  down  the  slopes. 

283.  Drainage  of  Snow  and  Ice.  —  Glaciers 
closely  resemble  rivers,  since  they  receive  the 
drainage  of  their  basins  through  the  solid  mate- 
rial which  flows  into  them ;  their  motion,  how- 
ever, is  much  slower.  Like  rivers,  they  have 
their  tributaries,  and  their  peculiarities  of  flow 
and  velocity. 

Several  glaciers  often  unite  and  flow  on  as  one 
mass ;  but  their  solid  condition  prevents  the  in- 
termingling which  occurs  in  rivers,  and  the  sepa- 
rate streams  can  generally  be  distinctly  traced 
throughout  the  remainder  of  their  course.  Like 
rivers,  the  top  and  middle  portions  move  more 
rapidly  than  the  sides  or  bottom,  owing  to  the 
diminished  friction. 

284.  Peculiarities  of  Glaciers. — The  surface 
of  the  glacier  is  often  comparatively  smooth ;  but 
when  irregularities  occur,  either  in  the  direction 
of  the  valley,  or  in  the  slope  of  its  bed,  the  glacier 
is  broken  into  deep  fissures,  called  crevasses.  These 
are  most  numerous  on  the  sides,  from  which  they 
extend  either  obliquely  up  the  stream,  or  directly 
across,  in  deep  transverse  fissures.  The  former 
are  generally  due  to  a  bend  in  the  valley,  one 
side  being  compressed  and  the  other  extended; 
the  latter,  to  steep  and  abrupt  descents  in  the  bed. 
Crevasses  are,  therefore,  rapids  in  the  ice  stream. 

Crevasses  vary  in  breadth  from  mere  crevices,  that  a 
knife-blade  can  scarcely  penetrate,  to  yawning  chasms 
over  100  feet  in  width.  The  depth  of  the  wider  crevasses 
is  generally  profound.  Their  vertical  walls  afford  a  con- 
venient opportunity  for  studying  many  peculiarities  of 
formation.  Looking  down  the  walls  of  the  crevasses,  the 
ice  appears  of  a  deep  azure  blue.  The  surface  ice  is  a  dirty 
white* 


HAIL,    SNOW,    AND    GLACIERS. 


1*09 


J- 


The  crevasses  gradually  disappear  below  the  cause  of 
disturbance,  the  fractures  rejoining  by  a  process  called 
regelation.  Regelation  is  the  property  which  fragments  of 
moist  ice  have  of  becoming  firmly  cemented  together,  when 
their  surfaces  are  brought  into  contact  under  pressure. 

The  water  derived  from  the  melting  of  the  ice 
issues  from  a  cavernous  arch  at  the  end  of  the 
glacier.  The  volume  of  the  issuing  stream,  which 
is  often  considerable,  is  dependent  on  the  tempera- 
ture, being  greater  during  the  warm  months  of 
the  year.  Many  rivers  have  their  origin  in  these 
glacier  streams ;  as,  the  Rhone  and  the  Rhine,  in 
Europe,  and  the  Ganges,  in  Asia. 

The  distance  the  glacier  extends  below  the  snow 
line  depends  on  the  mass  and  velocity  of  the  ice, 
and  the  rapidity  with  which  it  is  melted.  When 
the  winter  snows  are  light,  and  the  following  sum- 
mer unusually  warm,  the  end  of  the  glacier  re- 
treats up  the  mountain.  On  the  contrary,  heavy 
snowfalls  in  winter,  followed  by  a  cool  summer, 
permit  the  end  of  the  glacier  to  advance  far  into 
the  valley  below. 

285.  Transporting  Power  of  Glaciers. — All 
along  the  borders  of  the  valleys,  stones  and  dirt 
roll  down  the  declivities,  and,  accumulating  on 
the  surface  of  the  moving  mass,  are  carried  with 
it  to  a  lower  level.  These  accumulations  of  dirt 
and  stones  are  called  moraines;  they  are  most 
sharply  marked  at  the  sides  of  the  glaciers,  where 

:  they  are  called  lateral  moraines.  Where  two  gla- 
ciers flow  into  one  common  valley  a  moraine  called 
the  medial  moraine  marks  the  junction  of  their 
meeting  edges.s  At  the  end  of  the  glacier,  a  ter- 
minal moraine  extends  in  a  wide  curve  across  the 
valley.  Medial  moraines  are  sometimes  over  a 
hundred  feet  in  height.  Terminal  moraines  some- 
times attain  the  height  of  several  hundred  feet. 

The  masses  of  stone  transported  by  glaciers  are  often  of 
great  size.  Some  have  been  found  100  feet  long,  50  feet 
wide,  and  40  feet  high. 

286.  Erosion. — Such  immense  masses  of  ice 
must  deepen  considerably  the  valleys  through 
which  they  move.  When  they  have  deserted 
their  former  valleys,  evidences  of  their  previous 
existence  are  to  be  found  in  the  long  lines  of 
unstratified  rocks  and  mud  left  by  their  moraines 
and  boulders,  and  especially  in  the  deep  grooves, 
or  scratches,  cut  in  the  bottom  or  sides  of  the 
valleys  by  rocks  imbedded  in  the  moving  ice 
mass.  These  scratches  are  parallel,  and  show 
the  direction  of  the  motion. 

The  water  which  issues  from  the  terminal  cave  is  deeply 
charged  with  a  fine  sediment,  the  result  of  erosion.    This 


sediment  is  exceedingly  fertile,  and,  spread  out  by  the 
rivers  on  the  flood-grounds,  becomes  a  source  of  agricul- 
tural wealth. 

Fiords  and  Glacial  Lakes. — Valleys  cut  by 
glaciers  are  characterized  by  parallel  sides.  Gla- 
cial valleys,  when  formed  on  mountains  that  slope 
down  to  the  ocean,  if  the  region  is  subjected  to 
subsequent  depression  and  the  valleys  partially 
submerged,  are  penetrated  by  the  sea,  and  form 
arms  of  the  sea  extending  far  into  the  mountains. 
Such  valleys  are  called  fiords. 

The  following  are  the  most  important  fiord 
regions : 

(1.)  On  the  coasts  of  Norway. 

(2.)  On  the  western  coasts  of  the  Dominion  of 
Canada  and  Alaska. 

(3.)  On  the  coasts  of  Greenland,  where  the 
valleys  are  still  covered  with  ice  masses. 

The  numerous  lakes  of  glacial  regions  owe  their 
origin  either  to  the  erosion  of  softer  rocks,  or  to 
the  damming  up  of  rivers  by  the  terminal  mo- 
raines left  by  a  retreating  glacier. 

287.  Geographical  Distribution  of  Glaciers. — 
The  best  known  glacial  system  in  the  world  is 
found  in  Europe,  in  the  region  of  the  Central 
Alps.  Here  no  less  than  1100  glaciers  are  found, 
one  hundred  of  which  are  of  large  size. 

One  of  the  best  known  of  the  European  glaciers  is  that 
of  the  Mer  de  Glace  (Sea  of  Ice).  It  descends  from  the 
slopes  of  the  range  of  Mont  Blanc,  and  is  formed  by  the 
confluence  of  three  large  glaciers :  the  Glacier  du  Giant,  the 
Glacier  de  Lechaud,  and  the  Glacier  du  Talefre. 


Fig.  97.    The  Mer  de  Glace. 


Glaciers  occur  also  in  the  Pyrenees  Mountains ;  in  the 
Caucasus  range ;  and  in  the  Scandinavian  plateau,  from 
which  they  descend  into  the  Norwegian  fiords  to  less  than 
1000  feet  from  the  level  of  the  sea.  They  also  occur  in  the 
Patagonian  Andes 


110 


PHYSICAL    GEOGRAPHY. 


In  the  Arctic  zone  glaciers  are  particularly- 
numerous  and  extensive.  Here  they  generally 
reach  down  into  the  sea.  They  are  found  in  the 
islands  of  the  Arctic  Archipelago,  in  Greenland, 
Iceland,  Jan  Mayen,  and  Spitzbergen. 

The  Humboldt  Glacier,  in  Greenland,  is  sixty-nine  miles 
broad  at  its  lower  extremity  in  the  sea.  In  all  the  Arctic 
glaciers,  the  neve  region  is  more  extended  than  in  those 
of  more  southern  latitudes.  The  terminal  moraines  are 
found  at  the  bottom  of  the  sea,  near  the  foot  of  the 
glacier. 

In  the  lofty  mountain-ranges  of  the  Himalayas  and  in 
the  Karakorum,  occur  other  less  known,  though  exten- 
sive, regions  of  glaciers. 

288.  Icebergs. — When  the  glacier  extends  into 
the  sea,  the  base  is  undermined  by  the  warmer 
waters  of  the  ocean,  and  great  fragments  are 
broken  off  by  the  waves,  forming  floating  moun- 
tains of  ice,  called  icebergs.  Icebergs  are  particu- 
larly numerous  in  the  North  Atlantic,  into  which 
they  descend  from  the  extensive  Arctic  glacial 
region  already  described. 

The  limits  of  the  Arctic  and  Antarctic  drift  ice  are 
shown  in  the  map  of  the  isotherms. 


Fig.  98.    Icebergs. 

The  Ace  floes  of  the  polar  seas  have  their  origin 
in  the  snow  which  falls  into  the  cold  water,  re- 
maining partially  dissolved  and  subsequently 
freezing,  thus  adding  to  the  thickness  of  the  ice 
formed. 


289.  The  Glacial  Epoch  of  the  Earth.— Toward  the 
close  of  the  Mammalian  Age,  a  change  occurred  in  the  cli- 
mate of  the  earth,  and  extensive  glaciers  covered  most  of 
the  northern  continents,  reaching,  in  many  instances,  far 
toward  the  south.  In  the  United  States,  their  southern 
limit  appears  to  have  been  at  about  lat.  39°  N.,  in  Southern 
Pennsylvania,  Ohio,  Indiana,  Illinois,  and  Iowa.  In  Eu- 
rope, they  extended  as  far  south  as  the  50°  N.  lat.  In 
South  America,  they  probably  extended  as  far  toward  the 
equator  as  41°  S.  lat. 

The  evidences  of  the  existence  of  ancient  glaciers  are 
found  in  the  presence  of  accumulations  of  unstratified 
material,  called  the  drift;  in  the  presence  of  old  moraines; 
in  glacial  scratches  and  grooves  on  rocky  slopes ;  in  eroded 
valleys ;  and  in  the  presence  of  numerous  large  boulders, 
which  are  found  at  great  distances  from  their  places  of 
origin. 


o-FiHc 


CHAPTER   III. 

Electrical  and  Optical  Phenomena. 

290.  Nature  of  Electricity. — Electricity  is  now 
generally  believed  to  be  due  to  a  peculiar  wave 
motion  in  the  luminiferous  ether,  the  medium 
which  transmits  the  waves  of  light  and  heat. 

When  a  body  is  electrified  it  acquires  a  certain 
power  of  doing  work,  called  electric  potential. 
Electric  potential  is  measured  in  units  called 
volts.  The  path  through  which  an  electric  dis- 
charge passes  is  called  the  circuit.  All  circuits 
offer  a  measurable  resistance  to  the  passage  of  an 
electric  discharge.  Electric  resistance  is  meas- 
ured in  units  called  ohms. 

The  rate  at  which  electricity  passes  through  a 
circuit  is  called  the  current,  and  is  measured  in 
units  called  amperes.  An  ampere  is  the  current 
which  would  pass  in  a  circuit  whose  resistance  is 
one  ohm,  under  a  potential  of  one  volt. 

Though  electricity  is  probably  not  a  fluid,  yet  it  resem- 
bles a  fluid  in  many  respects,  and  the  units  already  re- 
ferred to  are,  to  a  certain  extent,  based  on  this  resem- 
blance. The  quantity  of  liquid  that  flows  through  a  pipe 
in  a  given  time  depends  on  the  pressure  on  the  liquid,  and 
the  resistance  offered  by  the  pipe.  The  quantity-per-sec- 
ond  corresponds  to  the  amperes ;  the  pressure  which  causes 
the  flow,  to  the  volts ;  and  the  resistance  which  limits  the 
flow,  to  the  ohms. 

Electricity  may  be  produced  in  bodies  by  a 
variety  of  causes :  such  as  friction,  heat,  chemical 
action,  magnetism,  and  animal  or  vegetable  life. 

There  are  two  distinct  forms  of  electrical  excitement : 
the  positive  and  the  negative.  A  body  with  a  high  potential 
is  generally  assumed  to  be  positively  charged  ;  one  with  a 
low  potential,  negatively  charged.  The  current  is  assumed 
to  flow  from  the  higher  to  the  lower  potential,  or  from  the 
positive  to  the  negative.    Bodies  charged  with  electricity 


ELECTRICAL    AND    OPTICAL    PHENOMENA. 


Ill 


of  the  same  kind,  repel  one  another ;  if  charged  with  dif- 
ferent kinds,  they  attract,  and  if  the  bodies  are  free  to 
move,  they  approach,  when  the  opposite  excitements  neu- 
tralize each  other.  In  case  the  electrical  excitement  is 
considerable,  the  union  is  accompanied  by  a  sharp  crack, 
and  a  flash  of  light,  called  the  electric  spark. 

291.  Conductors  of  electricity  are  bodies  which 
allow  its  ready  passage  through  them.  Metals, 
charcoal,  acids,  aqueous  solutions,  and  various 
animal  and  vegetable  substances,  are  good  con- 
ductors. Non-conductors  are  those  which  do  not 
allow  the  electricity  to  flow  freely  through  them. 
Gums,  resins,  glass,  silk,  and  dry  air  are  non-con- 
ductors. 

The  higher  the  conducting  power  of  a  circuit  the  lower 
will  be  its  resistance,  and,  consequently,  the  greater  the 
current  which  will  be  sent  through  it  by  a  given  poten- 
tial. 

292.  Atmospheric  Electricity. — Electric  excite- 
ment is  always  present  in  the  atmosphere.  The 
electricity  of  the  air  is  generally  positive,  although 
it  often  changes  rapidly  to  negative  on  the  ap- 
proach of  clouds  or  fogs.  It  is  feeblest  within  a 
few  feet  of  the  surface,  and  increases  with  the 
elevation  above  the  general  surface  of  the  earth. 

Origin  of  Free  Atmospheric  Electricity. — The  elec- 
tricity of  the  atmosphere  is  caused  by  a  variety  of  circum- 
stances, the  chief  of  which  are  evaporation  and  condensa- 
tion ;  unequal  heating  of  the  earth  by  the  sun's  rays ; 
combustion ;  animal  and  vegetable  life ;  and  the  friction 
of  winds  against  each  other  or  against  the  earth's  sur- 
face. 

293.  Lightning  occurs  when  the  electricity  of 
a  cloud  discharges  to  the  earth  or  to  a  neighbor- 
ing cloud.  The  discharge  is  attended  by  a  vivid 
spark,  called  lightning.  The  destructive  effects 
of  lightning  are  due  to  the  discharge  between  the 
clouds  and  the  earth. 

Thunder. — The  heat  of  the  spark  vaporizes  the 
rain-drops,  and  enormously  expands  the  air,  pro- 
ducing, on  their  subsequent  cooling,  a  partial 
vacuum,  which  is  further  increased  by  the  mo- 
mentary pushing  aside  of  the  air  by  the  discharge. 
The  surrounding  air  rushing  violently  into  this 
vacuum  produces  the  sound  called  thunder. 

The  potential  of  the  lightning  flash  is  enormously  higher 
than  that  produced  by  artificial  means,  and  must  be  equal 
to  many  millions  of  volts.  This  high  potential  is  due  to 
the  enormous  decrease  in  the  surface  of  a  single  rain-drop 
from  the  thousands  of  smaller  drops  which  have  coalesced 
to  form  it. 

294.  Varieties  of  Lightning.— There  are  five  varieties 
of  lightning :  zig-zag  or  chain,  sheet,  heat,  globular,  and  vol- 
canic lightning. 

Zig-zag  Lightning  probably  owes  its  forked  shape  to 
the  resistance  which  the  air  offers  to  its  passage  through 


it.  The  air-particles,  being  crowded  together  in  the  path 
of  the  spark,  the  lightning  darts  to  one  side,  where  the  air 
is  less  dense. 

Sheet  Lightning  generally  accompanies  thunder- 
storms, and  appears  as  an  expanded  flashs  which  illu- 
mines the  clouds. 

Heat  Lightning,  or  lightning  without  thunder,  is  gener- 
ally seen  near  the  horizon,  during  hot  weather.  It  is 
probably  caused  by  the  reflection  of  lightning  from  a 
storm  below  the  horizon. 

Globular  Lightning.  On  rare  occasions,  the  lightning 
appears  in  the  form  of  a  globe  of  light,  which  remains 
stationary  in  the  air  or  moves  slowly  through  it.  Its 
cause  is  unknown. 

Volcanic  Lightning.  During  the  eruption  of  volca- 
noes, vivid  flashes  of  lightning  often  occur  in  the  air  near 
the  craters.  Volcanic  lightning  is  probably  caused  by  the 
rapid  condensation  of  the  vast  volumes  of  vapor  emitted 
with  the  ashes  and  lava. 

295.  Lightning  Rods,  invented  by  Franklin, 
protect  the  buildings  on  which  they  are  placed,  by 
quietly  discharging  the  electricity  from  the  over- 
hanging cloud.  They  generally  effect  this  by  an 
opposite  electricity  passing  from  the  earth  up  the 
rod,  and  neutralizing  that  of  the  cloud.  Unless 
the  rods  are  placed  in  good  metallic  connection 
with  the  earth,  and  with  all  conductors  near 
them,  they  are  sources  of  danger  rather  than  of 
protection. 

296.  St.  Elmo's  Fire. — When  the  atmosphere 
is  highly  charged  with  electricity,  faint  tongues 
of  fire  are  often  seen  on  the  ends  of  bodies  in 


Pig.  99.    St.  Elmo's  Fire. 

connection  with  the  earth,  like  the  masts  of  ships, 
steeples,  etc.,  due  to  an  electric  discharge,  known 
as  the  brush-discharge.  They  are  called  St.  Elmo's 
fire,  and  are  harmless. 


112 


PHYSICAL    GEOGRAPHY. 


297.  The  Aurora  Borealis,  or  northern  light, 
is  a  phenomenon  of  marvellous  beauty,  occurring 
in  the  sky  of  high  latitudes  in  both  the  northern 
and  southern  hemispheres.  It  appears  in  a  va- 
riety of  forms ;  at  times  huge  pillars  of  fire  move 
rapidly  across  the  heavens,  or  the  entire  northern 
sky  is  lighted  as  by  a  drifting  storm  of  luminous 
snow.  The  commonest  appearance,  however,  is 
that  of  an  arch  of  fire,  from  which  streamers 
flash  toward  the  zenith. 

Auroras  are  most  frequent  in  high  latitudes, 
though  not  in  the.  immediate  vicinity  of  the 
poles. 

Auroras  are  caused  by  the  passage  of  electricity  through 
the  rare  air  of  the  upper  regions.  The  proofs  are  as  fol- 
lows :  During  the  continuance  of  an  aurora,  the  telegraph 
wires  show  the  presence  of  an  unusual  electrical  disturb- 
ance, and  the  magnetic  needle  is  subject  to  frequent  oscil- 
lations; moreover,  the  same  phenomena  can  be  produced 
by  the  passage  of  an  electrical  current  through  rarefied 
gases,  as  in  the  Geissler  tubes — different  colors  arising 
from  its  passage  through  different  gases. 


Fig.  100.    Aurora  Borealis. 

298.  Magnetism. — The  recent  researches  of 
Herz  leave  little  doubt  that  electro-magnetic  phe- 
nomena are  due  to  a  wave  motion  in  the  lumi- 
niferous  ether. 

Magnets  are  bodies  which  have  the  power  of 
attracting  particles  of  iron  or  the  opposite  poles 
of  other  magnets. 

All  magnets  possess  an  atmosphere  of  influence 
surrounding  them,  called  the  magnetic  field.  The 
magnetic  field  is  traversed  by  lines  of  force,  which 
come  out  of  the  magnet  at  one  point  and  enter  it 
at  another,  thus  forming  a  magnetic  circuit.     The 


points  where  the  lines  come  out  are  called  poles ; 
the  former  being  the  positive  or  north  pole,  and 
the  latter  the  negative  or  south  pole. 

Magnets  are  either  natural  or  artificial.  Nat- 
ural magnets  are  found  in  lodestone,  a  species  of 
iron  ore  composed  of  oxygen  and  iron.  Pieces 
of  hardened  iron  or  steel  may  be  magnetized,  by 
rubbing  them  with  a  lodestone,  or  by  passing 
electrical  currents  around  them,  thus  forming 
what  are  called  electro-magnets.  All  magnetiz- 
able substances  become  magnetized  when  they 
are  brought  into  a  magnetic  field. 

If  a  magnetized  bar  or  needle  be  suspended  at 
its  centre  of  gravity  so  as  to  move  freely  in  a 
horizontal  plane,  after  a  few  oscillations  it  will 
come  to  rest,  with  one  of  its  ends  pointing  nearly 
to  the  geographical  north  pole  of  the  earth.  This 
end  of  the  magnet  is  called  its  north  pole,  the  op- 
posite end  its  south  pole,  and  the  magnet  itself,  a 
magnetic  needle. 


Fig.  101.    The  Magnetic  Needle. 

299.  Magnetic  Attractions  and  Repulsions. — If  a 
magnet  is  brought  near  a  magnetic  needle,  attraction  or 
repulsion  will  ensue — repulsion,  when  the  poles  are  of  the 
same  name;  attraction,  when  they  are  of  opposite  names. 
Thus,  when  a  north  pole  is  approached  to  a  north  pole,  or 
a  south  pole  to  a  south  pole,  they  repel  each  other;  but 
when  a  north  pole  is  approached  to  a  south  pole,  or  a  south 
pole  to  a  north  pole,  they  attract.  If  the  approaching 
magnet  is  powerful,  it  will  deflect  the  magnetic  needle, 
although  several  feet  distant  from  it ;  and  if  placed  per- 
manently in  this  position,  the  magnetic  needle  will  n» 
longer  point  to  the  north,  but  will  turn  toward  the  disturbing 
magnet. 

300.  Cause  of  the  Magnetic  Needle  pointing  to 
the  Geographical  North. — The  magnetic  needle 
points  to  the  north  for  the  same  reason  that  the 
opposite  poles  of  magnets  point  to  each  other 
when  they  are  sufficiently  near.  The  entire  earth 
acts  as  one  huge  magnet,  with  its  poles  in  the  neigh- 
borhood of  the  extremities  of  its  axis,  and  the  mag- 
netic needle  points  toward  these  poles  on  account 
of  their  attraction. 


ELECTRICAL    AND    OPTICAL    PHENOMENA. 


113 


The  earth,  like  all  magnets,  possesses  a  magnetic  field. 
Lines  of  magnetic  force  come  out  of  its  north  pole,  pass 
around  the  earth  through  the  air,  and  enter  the  earth  at 
its  south  pole.  A  magnetic  needle,  placed  in  the  earth's 
field,  if  free  to  move,  will  come  to  rest  with  the  earth's 
lines  of  force  passing  into  its  south  pole  aud  passing  out  of 
its  north  pole.  That  pole  of  the  needle  which  points  to 
the  geographical  north  is,  therefore,  of  opposite  magnetic 
polarity  to  the  earth's  polarity  in  the  Northern  Hemi- 
sphere. In  the  United  States,  the  Northern  Hemisphere 
is  regarded  as  possessing  south  magnetic  polarity;  in 
France,  as  possessing  north  magnetic  polarity. 

301  Origin  of  the  Earth's  Magnetism. — The 
exact  cause  of  the  earth's  magnetism  is  unknown. 
Currents  of  electricity  circulating  around  a  con- 
ductor render  it  a  magnet.     Electrical  currents 


are  generated  in  nearly  all  substances,  when  they 
are  unequally  heated.  The  earth  appears  to  owe 
its  magnetism  to  the  circulation  around  it  of  cur- 
rents of  electricity,  produced,  most  probably,  by 
the  unequal  heating  of  different  portions  of  its 
surface  by  the  sun's  rays.  These  currents  would 
follow  the  sun  in  its  apparent  motion  from  east 
to  west.  Since  the  earth's  magnetism  appears  to 
have  its  remote  cause  in  the  sun's  heat,  variations 
in  the  temperature  should  be  followed  by  corre- 
sponding variations  in  the  intensity  of  magnetism. 
This  is  found  to  be  the  case. 

Magnetic    storms,    or    unusual   variations    in 
the    earth's    magnetism,   have    been   noticed  to 


Fig.  102.    Declination  Chart. 
(West  Declination  is  represented  by  the  continuous  lines  ;  East  Declination  by  the  dotted  lines ;  the  Agones  by  the  heavy  lines.) 


correspond  with  outbursts  of  solar  activity,  as 
manifested  by  the  unusual  occurrence  of  new 
spots. 

302.  The  Declination  or  Variation  of  the  Nee- 
dle.— The  earth's  magnetic  poles  do  not  corre- 
spond with  its  geographical  poles.  The  magnetic 
needle,  therefore,  except  in  a  few  localities,  does 
not  point  to  the  true  geographical  north,  but  to 
the  east  or  to  the  west  of  it.  This  deviation  from 
the  true  north  is  called  the  declination  or  vari- 
ation, and  is  east  or  ivest  according  as  the  needle 
points  to  the  east  or  the  west  of  the  true  or  geo- 
graphical north.  The  amount  of  this  variation 
differs  in  different  parts  of  the  earth. 


The  position  of  the  magnetic  poles  of  the  earth  is  not 
always  the  same,  but  cnanges  slowly  from  year  to  year, 
thus  producing  corresponding  changes  in  the  declination 
of  the  needle.  This  change  is  called  secular  variation.  The 
needle,  at  any  place,  points  more  and  more  to  the  east, 
following  the  change  of  the  poles.  At  length,  after  a  long 
period,  it  becomes  stationary,  and  then  begins  to  move 
toward  the  true  meridian,  which  it  at  length  reaches ; 
when,  continuing  its  motion,  the  declination  becomes 
west. 

Isogonal  Lines. — Lines  connecting  places  which 
have  the  same  declination,  are  called  isogonal  lines. 
Lines  connecting  these  places,  when  the  needle 
points  to  the  true  north,  are  called  agones,  or  lines 
of  no  declination. 

The  direction  of  the  isogonal  lines  is  shown  in  the  de- 


114 


PHYSICAL    GEOGRAPHY. 


clination  chart,  the  figures  near  the  lines  giving  the  value 
of  the  declination  in  degrees.  The  agone  in  each  hemi- 
sphere is  marked  0.  In  the  New  World  it  enters  South 
America  near  Rio  Janeiro,  curves  to  the  eastward  around 
the  Antilles,  passes  near  Washington,  through  the  western 
part  of  Hudson  Bay,  and  enters  the  magnetic  pole  at 
Boothia  Felix.  The  agone,  in  the  Old  World,  passes 
through  the  west  of  Australia,  near  the  western  coasts 
of  Hindostan,  through  Persia,  the  eastern  part  of  the  Cas- 
pian Sea,  and  through  the  White  Sea,  in  Europe.  The 
oval  curves  in  Eastern  Asia  seem  to  indicate  a  secondary 
magnetic  pole. 

In  nearly  all  Europe,  in  the  whole  of  Africa  and  Arabia, 
in  eastern  North  and  South  America,  and  in  nearly  all  the 
Atlantic  and  Indian  Oceans,  the  declination  is  west.  It  is 
also  west  along  part  of  the  eastern  shores  of  Asia,  around 
the  secondary  magnetic  pole.  In  the  remainder  of  the 
world  the  declination  is  east. 

303.  The  Inclination  or  Dip  of  the  Needle. — 
The  lines  of  force  of  the  earth's  magnetic  field 
are  in  most  places  inclined  to  the  earth's  surface. 
The  position  of  the  needle  is,  therefore,  horizontal 
in  but  a  few  localities.  In  most  places,  one  of  the 
poles  is  inclined  to  the  earth.  This  is  called  the 
inclination  or  dip  of  the  needle.  In  the  Northern 
Hemisphere,  it  is  the  north  pole,  and  in  the  south- 
ern, the  south  pole  that  is  inclined. 

304.  Magnetic  Equator. — The  angle  of  dip  is 
greater,  the  nearer  we  approach  either  magnetic 
pole.  At  the  pole,  the  needle  points  vertically 
downward ;  midway  between  the  poles,  the  needle 
is  horizontal ;  the  last  position  is  called  the  mag- 
netic equator. 

Lines  connecting  places  which  have  the  same  angle  of 
dip  are  called  isoclinal  lines.  They  correspond  in  a  very 
remarkable  manner  with  the  isothermal  lines.  This  seems 
to  show  the  dependence  of  the  intensity  of  magnetism  on 
the  distribution  of  the  sun's  heat.  The  inclination  is  also 
subject  to  secular  changes,  like  the  declination. 

305.  Optical  Phenomena  are  caused  by  changes 
in  the  direction,  intensity,  or  composition  of  sun- 
light during  its  passage  through  the  atmosphere. 

Sunlight,  when  passed  through  a  prism,  is  dis- 
persed or  separated  into  a  great  number  of  differ- 
ent colored  lights.  The  following  seven  groups  of 
colors  are  prominent :  violet,  indigo,  blue,  green, 
yellow,  orange,  and  red.  These  are  called  the  pris- 
matic colors,  or,  collectively,  a  spectrum.  They 
differ  in  the  ease  with  which  they  are  refracted, 
or  turned  out  of  their  course,  in  passing  from 
one  medium  to  another  of  different  density.  The 
above  prismatic  colors  seen  in  the  spectrum  are 
name4  m  the  order  of  their  refrangibility,  begin- 
ning with  the  violet,  the  most  refrangible,  and 
ending  with  the  red,  the  least  refrangible. 

306.  Rainbows  are  arches  of  the  prismatic 
colors,   caused   by   the   dispersion   of   the   light 


during  its  passage  through  the  falling  drops  of 
rain.  The  rays  entering  the  drop,  are  reflected 
from  the  surfaces  farthest  from  the  sun,  and 
emerge  separated  into  the  prismatic  colors. 

Rainbows  are  seen  when  the  observer  stands 
with  his  back  toward  the  sun.  They  are  largest 
when  the  sun  is  nearly  setting. 

A  secondary  bow  sometimes  occurs  outside  the 
primary,  with  the  order  of  its  colors  reversed. 
It  is  caused  by  the  light  which  is  twice  reflected 
from  the  back  of  the  drops. 

307.  The  Sunset  Tints  of  the  Sky  are  yellow, 
orange,  and  red.  The  rays  of  the  setting  sun  are 
dispersed,  during  their  passage  through  the  clouds, 
or  through  accumulations  of  vapor  at  the  horizon, 
and  only  the  colors  that  are  least  turned  out  of 
their  course,  the  yellow,  the  orange,  and  the  red, 
pass  through  and  light  up  the  western  sky. 

308.  The  Blue  Color  of  the  Sky  is  caused  by 
the  diffusion  through  the  air  and  their  subsequent 
reflection  from  its  particles  of  the  more  refrangi- 
ble rays  of  light :  the  indigo  and  the  blue. 

309.  Halos  and  Coronae  are  rings  of  prismatic 
colors  surrounding  the  sun  and  moon. 

Halos  are  caused  by  the  presence  in  the  air 
of  small  crystals  of  ice  or  snow.  Parhelia,  or 
mock  suns,  and  Paraselenoz,  or  mock  moons 
(bright  spots  which  somewhat  resemble  suns  and 
moons),  are  frequently  seen  where  the  complicated 
circles  of  halos  intersect  each  other.  Coronce  are 
circles  of  light,  seen  most  frequently  around  the 
moon.  They  are  caused  by  the  presence  of  a 
small  quantity  of  condensed  vapor  in  the  air. 
They  generally  indicate  changes  in  the  weather. 


Fig.  103.    Halo. 

310.  The  Mirage  is  a  general  term  applied  to 
the  appearance  which  objects  present  when  viewed 
by  means  of  rays  of  light  that  have  passed  through 


SYLLABUS. 


115 


strata  of  air,  which  gradually  increase  or  decrease 
in  density.  In  this  way  the  objects  appear  either 
inverted  or  erect,  but  always  out  of  their  true 
position.  Sometimes  the  objects  are  repeated,  one 
being  seen  above  the  other.  The  mirage  occurs 
both  over  water  and  land.  It  is  caused  by  the 
turning  of  the  rays  of  light  out  of  their  original 
direction. 

The  Mirage  of  the  Desert  occurs  over  hot,  arid 
surfaces,  whenever  the  strata  of  air  increase  rap- 
idly in  density  from  the  surface  upward.  The 
rays  of  light  from  distant  objects,  such  as  trees, 
are  reflected  from  one  of  the  lower  layers  of  air, 


and,  entering  the  eye  of  the  observer,  appear  to 
come  from  inverted  objects,  which  seem  to  be 
surrounded  by  a  sheet  of  water.  The  image  of 
a  real  tree  is  seen,  but  out  of  its  true  situation,  so 
that  when  the  observer  reaches  the  place  he  finds 
nothing. 

The  mirage  frequently  occurs  on  the  sea.  Ves- 
sels that  are  too  far  below  the  horizon  to  be  di- 
rectly visible,  become  visible  by  refraction.  This 
phenomenon  is  called  looming.  The  vessels  are 
seen  both  erect  and  inverted,  and  sometimes  ap- 
pear suspended  in  the  clouds.  Distant  islands 
are  sometimes  visible  from  the  same  cause. 


SYLLABUS. 


-<x£»<c 


The  rapidity  of  evaporation  increases — 1.  With  the  tem- 
perature of  the  atmosphere.  2.  With  the  extent  of  sur- 
face exposed.  3.  With  a  decrease  in  the  quantity  of  va- 
por already  in  the  air.  4.  With  the  renewal  of  the  air ; 
and,  5.  With  a  decrease  of  the  pressure  on  the  surface. 

When  air  can  hold  no  more  moisture  in  an  invisible 
state,  it  is  said  to  be  saturated  or  at  its  dew  point. 

Whenever  the  air  is  lowered  below  the  temperature  of 
its  dew  point,  its  moisture  is  deposited  as  cloud,  mist, 
snow,  hail,  sleet,  or  rain. 

More  dew  falls  on  clear  nights,  when  the  wind  is  mod- 
erate, than  on  cloudy  nights,  when  the  wind  is  high. 

In  fogs,  mists,  and  clouds,  the  moisture  is  condensed  as 
minute  drops. 

Clouds  owe  their  variety  of  forms  to  the  action  of  aerial 
currents,  and  their  constant  tendency  to  settle.' 

The  dense  fogs  so  common  off  the  banks  of  Newfound- 
land are  caused  by  the  chilling  of  the  warm,  moist  air  of 
the  Gulf  Stream  by  the  cooler  air  of  the  Labrador  cur- 
rent. 

The  primary  forms  of  clouds,  are  the  cirrus,  the  cumu- 
lus, the  nimbus,  and  the  stratus. 

The  secondary  forms  of  clouds,  are  the  cirro-stratus,  the 
cirro-cumulus,  and  the  cumulo-stratus. 

Rain  falls  whenever  the  temperature  of  a  mass  of  air  is 
lowered  considerably  below  the  temperature  of  its  dew 
point. 

This  reduction  of  temperature  may  occur  —  1.  By  a 
change  of  altitude  by  means  of  ascending  currents.  2. 
By  a  change  of  latitude,  as  by  the  warm  equatorial  cur- 
rents flowing  into  colder  regions  nearer  the  poles.  3.  A 
comparatively  small  rainfall  may  be  caused  by  the  inter- 
mingling of  moist  cold  and  moist  warm  air. 

As  a  rule,  the  equatorial  currents  bring  rain,  the  polar 
currents,  drought. 

In  the  zone  of  calms,  it  rains  during  the  hottest  part  of 
the  day,  or  in  the  afternoon,  when  the  ascending  currents 
are  strongest. 

In  the  zone  of  the  trades,  it  rains  during  the  hottest 
part  of  the  year,  or  in  summer. 
14 


Between  lat.  24°  and  30°,  both  N.  and  S.,  the  rainfall  is 
scanty,  and  in  some  localities  almost  absent. 

In  the  zone  of  the  variables,  it  may  rain  at  any  hour  of 
the  day  or  night,  or  at  any  time  of  the  year. 

In  the  polar  zones,  the  winters  are  clear;  snows  and 
drizzling  rains  occur  in  spring  and  autumn. 

Between  lat.  30°  and  35°,  both  N.  and  S.,  it  is  dry  in 
summer  during  the  prevalence  of  the  polar  currents.  The 
rest  of  the  year  is  wet. 

The  rainfall  of  any  place  is  determined  by  means  of  an 
instrument  called  a  rain-gauge  or  pluviometer. 

An  inch  of  rain  on  the  surface  of  a  square  yard  is  equal 
in  weight  to  46.75  pounds ;  an  inch  on  the  surface  of  an 
acre,  to  the  weight  of  about  100  tons. 

The  quantity  of  rain  decreases  from  the  equator  to  the 
poles,  and  from  the  coasts  of  the  continents  toward  the 
interior. 

More  rain  falls  on  mountains  than  on  plains ;  more  on 
plains  than  on  plateaus;  more  in  the  Northern  Hemi- 
sphere than  in  the  Southern. 

In  the  tropics  of  the  New  World,  the  annual  rainfall  is 
115  inches;  in  the  Old  World,  only  77  inches. 

In  the  temperate  regions  of  the  New  World,  the  annual 
rainfall  is  35  inches ;  in  the  Old  World,  but  34  inches. 

The  average  rainfall  of  Europe,  between  lat.  36°  and  60° 
N.,  is  34  inches. 

The  average  rainfall  in  the  United  States,  between  24° 
30'  and  45°  north  latitude,  is  39  inches. 

The  desert  belt  of  the  eastern  continent  extends  from 
the  western  shores  of  Northern  Africa  eastward  to  the 
Great  Kinghan  Mountains  in  Asia.  It  includes  the  Sa- 
hara, the  Arabian  and  Persian  Deserts,  and  the  Desert  of 
Mongolia.  The  aridity  of  this  immense  tract  is  caused  by 
the  absence  of  rain. 

The  desert  tracts  near  the  summits  of  high  mountains 
are  caused  by  the  absence  of  heat  and  liquid  moisture. 

Hail  falls  when  bodies  of  warm  and  intensely  cold  air 
are  rapidly  commingled. 

Snow  falls  when  the  moisture  is  condensed  at  tempera- 
tures at  or  below  32°  Fahr.,  under  conditions  favorable  to 


116 


PHYSICAL    GEOGRAPHY. 


gradual  crystallization  while  the  moisture  is  condensing. 
Sleet  is  frozen  rain. 

The  snow  line  is  the  distance  above  the  sea  where  snow 
remains  throughout  the  year. 

The  snow  line  in  the  tropics  is  found  at  about  three 
miles  above  the  level  of  the  sea ;  in  the  temperate  regions, 
at  rather  less  than  two  miles ;  near  the  northern  extremi- 
ties of  the  continents,  at  less  than  one  mile ;  while  still 
farther  north,  on  the  polar  islands,  it  is  but  a  few  hundred 
feet  above  the  sea. 

The  height  of  the  snow  line,  depends — 

(1.)  On  the  amount  of  the  snowfall. 

(2.)  On  the  temperature  of  the  valley. 

(3.)  On  the  inclination  of  the  slopes. 

Glaciers  are  immense  masses  of  ice,  formed  by  the  snow 
which  accumulates  on  the  slopes  of  mountains  above  the 
snow  line.  They  move  slowly  by  gravity  down  the  moun- 
tain slopes,  bearing  with  them  accumulations  of  dirt  and 
stones,  called  moraines. 

The  upper  surface  of  the  glacier  is  generally  broken  into 
deep  fissures,  called  crevasses. 

The  water  derived  from  the  melting  of  the  glacier  issues 
in  a  stream  from  the  lower  end  of  the  ice  mass.  It  is 
highly  charged  with  sediment  derived  from  the  erosion 
of  the  glacier.  It  often  forms  the  source  of  a  powerful 
river. 

The  following  mountains  contain  glaciers :  the  Alps,  the 
Pyrenees,  the  Caucasus,  the  Scandinavian  Mountains,  the 
Himalayas,  and  the  Karakorum. 

When  glaciers  descend  into  the  sea,  the  waters  under- 
mine them,  and  detach  huge  masses,  which  float  away  to 
great  distances.    These  masses  are  called  icebergs. 

Toward  the  close  of  the  Mammalian  Age,  a  change  oc- 
curred in  the  climate  of  the  earth,  by  which  all  the  north- 
ern continents  were  covered  with  glaciers. 

The  unit  of  electric  potential  is  called  a  volt ;  the  unit 
of  current  is  called  an  ampere;  the  unit  of  resistance  is 
called  an  ohm. 

Comparing  the  flow  of  electricity  to  that  of  a  current 
of  water  in  a  pipe,  the  volt  corresponds  to  the  pressure 
causing  the  flow,  the  ohm  to  the  friction  or  other  resist- 


ance opposing  it,  and  the  ampere  to  the  quantity  of  the 
flow  per  second. 

The  free  electricity  of  the  air  is  generally  positive. 

Lightning  results  when  the  electricity  of  a  cloud  dis- 
charges to  the  earth,  or  to  a  neighboring  cloud. 

There  are  five  kinds  of  lightning:  zig-zag,  heat,  sheet, 
globular,  and  volcanic. 

When  the  air  contains  an  unusually  great  quantity  of 
electricity,  faintly  luminous  balls  are  seen  on  the  ends  of 
tall  objects.    These  are  called  St.  Elmo's  fire. 

Auroras  are  caused  by  the  passage  of  electricity  through 
the  rare  air  of  the  upper  regions  of  the  atmosphere. 

The  earth  acts  like  a  huge  magnet.  It  possesses  a  mag- 
netic field,  and  has  lines  of  force  entering  its  south  pole 
in  the  Northern  Hemisphere,  and  coming  out  of  its  north 
pole  in  the  Southern  Hemisphere. 

A  magnetic  needle,  if  free  to  move,  will  come  to  rest  in 
the  earth's  field  with  the  lines  of  force  of  the  earth  pass- 
ing in  at  its  south  pole  and  coming  out  at  its  north  pole. 

The  magnetic  needle  points  to  the  north,  from  the  action 
of  the  magnetic  poles  of  the  earth.  The  cause  of  the 
earth's  magnetism  is  not  certainly  known.  It  is  probably 
due  to  electrical  currents  which  circulate  around  it. 

Magnetic  storms,  or  unusual  variations  in  the  earth's 
magnetism,  correspond  with  outbursts  of  solar  activity 
as  manifested  by  sun-spots. 

The  deviation  of  the  needle  from  the  true  north,  is 
called  its  declination;  the  deviation  from  a  horizontal 
plane,  its  inclination.  Both  declination  and  inclination 
are  subject  to  diurnal,  annual,  and  secular  variations. 

Isogonal  lines  connect  places  which  have  the  same  dec- 
lination. Isoclinal  lines  connect  places  which  have  the 
same  inclination.  Isoclinal  lines  are  nearly  coincident 
with  the  isothermal  lines. 

Rainbows  are  caused  by  the  action  of  light  on  falling 
raindrops. 

Halos  are  caused  by  snow  crystals  in  the  air ;  Coronse,  by 
minute  particles  of  water. 

The  Mirage  is  caused  by  the  bending  of  the  rays  of  light 
from  their  original  direction,  while  passing  from  one  me- 
dium to  another  of  different  density. 


REVIEW   QUESTIONS. 


What  do  you  understand  by  evaporation  ? 

Name  the  circumstances  upon  which  the  rapidity  of 
evaporation  depends. 

Define  dew  point. 

What  condition  is  necessary  in  order  that  the  invisible 
moisture  of  the  atmosphere  may  become  visible  in  any 
form  of  precipitation  ? 

Under  what  circumstances  is  dew  deposited  ? 

Why  is  more  dew  deposited  on  a  clear  night  than  on 
a  cloudy  night?  Why  is  more  dew  deposited  on  a  still 
night  than  on  a  windy  one? 

Under  what  circumstances  are  fogs,  or  mists,  produced  ? 
How  do  fogs  or  mists  differ  from  clouds? 

What  is  the  condition  of  the  particles  of  water  which 
form  the  clouds?  Are  they  minute  drops,  or  hollow  vesi- 
cles? 

Describe  the  appearance  of  the  cirrus  cloud.  How  does 
its  height  compare  with  that  of  other  clouds  ? 

During  what  parts  of  the  day  are  stratus  clouds  most 
common  ?    To  what  do  they  owe  their  banded  appearance  ? 


Describe  the  cumulus  cloud.  During  what  part  of  the 
day  is  it  most  common? 

Why  should  the  cirro-stratus  clouds  generally  indicate 
approaching  rain  ? 

Name  three  conditions  under  which  rain  may  be  caused. 
By  which  are  the  heaviest  rains  generally  produced? 

Are  the  equatorial  currents  likely  to  bring  rain  or 
drought?    The  polar  currents?    Why? 

Name  the  periodical  rain  zones. 

When  does  it  rain  in  the  zone  of  calms?  In  the  zone 
of  the  trade  winds?    Why? 

In  what  portions  of  the  zone  of  the  variable  winds  is 
the  rainfall  approximately  periodical? 

Describe  the  rainfall  in  the  zone  of  the  variable  winds. 
In  the  zone  of  the  polar  winds. 

Describe  the  construction  of  a  rain-gauge  or  pluvi- 
ometer. 

Why  should  more  rain  fall  on  a  mountain  than  on  the 
lowlands  at  its  base?  Why  should  more  rain  fall  on  the 
coasts  of  a  continent  than  in  the  interior? 


REVIEW    AND    MAP    QUESTIONS. 


117 


Compare  the  mean  annual  rainfall  of  the  tropics  of  the 
Old  and  New  Worlds.  Of  the  temperate  regions  of  the 
Old  and  New  Worlds. 

Name  the  rainless  districts  of  the  Eastern  Continent. 
Of  the  Western  Continent. 

What  is  the  cause  of  the  almost  total  abserce  of  rain  in 
these  districts  ? 

Under  what  circumstances  is  hail  produced  ? 

Describe  the  structure  of  a  hailstone. 

Explain  the  rotary  theory  of  hail. 

Define  the  snow  line.  Upon  what  does  the  height  of 
the  snow  line  depend?  At  what  height  above  the  sea- 
level  is  it  found  in  the  tropics?  In  the  temperate  re- 
gions?   In  the  polar  zones? 

How  are  glaciers  formed?  In  what  respects  do  they 
resemble  rivers? 

What  are  crevasses  ?    How  are  they  formed  ? 

Name  some  rivers  which  take  their  origin  in  the  melt- 
ing of  glacial  ice. 

Define  lateral  moraines;  medial  moraines;  terminal 
moraines. 

Explain  the  manner  in  which  fiord-valleys  were 
formed.  What  is  the  probable  origin  of  lakes  in  all 
glacier  districts? 

Name  some  of  the  European  mountain  systems  which 
contain  extended  glacier  regions.  Name  two  Asiatic 
mountain  ranges  which  contain  such  regions. 


How  are  icebergs  formed  ?  Is  the  ice  of  which  they  are 
composed  salt  or  fresh  ? 

What  are  ice  floes  ?    State  their  origin. 

What  appears  to  have  been  the  southern  limit  of  the 
glaciers  in  the  United  States,  during  the  glacial  epoch, 
which  occurred  toward  the  close  of  the  Mammalian  Age  ? 

What  is  the  origin  of  free  atmospheric  electricity  ? 

Define  volt ;  ohm ;  ampere ;  potential ;  circuit. 

Under  what  circumstances  does  lightning  occur?  What 
is  the  cause  of  the  accompanying  thunder? 

Name  five  varieties  of  lightning. 

By  what  are  auroras  caused  ? 

What  is  the  cause  of  the  directive  tendency  of  the  mag' 
netic  needle  ? 

What  is  believed  to  be  the  cause  of  the  earth's  magnet- 
ism? 

What  do  you  understand  by  the  earth's  magnetic  field  ? 

Define  isogonal  lines ;  isoclinal  lines. 

With  what  lines  are  the  isoclinal  lines  nearly  coinci- 
dent ? 

Explain  the  phenomenon  of  the  rainbow. 

What  is  the  cause  of  the  sunset  tints  of  the  sky  ?  Of 
the  blue  color  of  the  sky? 

What  are  halos  and  coronse  ?    By  what  are  they  caused  ? 

Explain  the  cause  of  the  mirage  of  the  desert. 

What  do  you  understand  by  the  phenomena  of  loom- 
ing? 


MAP  QUESTIONS. 


►oXXc 


Trace  on  the  map  of  the  winds  and  rains,  the  portions 
of  the  world  included  in  the  zone  of  calms.  When  does 
it  rain  in  the  zone  of  calms  ? 

Trace  in  a  similar  manner  the  portions  included  in 
the  zones  of  the  trades,  and  the  zones  of  the  variables. 
What  is  characteristic  of  the  rainfall  in  each  of  these 
zones  ? 

Why  should  the  eastern  shores  of  tropical  South  Amer- 
ica be  moist,  and  the  western  dry? 

To  what  peculiarity  of  position  does  Northern  Africa 
owe  its  scanty  rainfall? 


Trace  on  the  map  of  the  isothermal  lines  the  southern 
limit  of  the  Arctic  drift  ice;  the  northern  limit  of  the 
Antarctic  drift  ice. 

Trace  on  the  declination  chart,  the  agone,  or  line  of  no 
declination,  in  the  Western  Hemisphere. 

Trace  "the  line  of  no  declination  in  the  Eastern  Hemi- 
sphere. What  smaller  line  of  no  declination  exists  in  this 
hemisphere  ? 

Notice  that  in  the  Western  Hemisphere  the  isogonal 
lines  all  meet  in  a  point  near  Hudson  Bay.  What  does 
this  meeting  indicate? 


Part  Y. 

ORGANIC    LIFE. 


-*o^c 


The  variety  and  luxuriance  of  life  found  on  the  surface  of  the  earth  are  far  greater  than  is  at 
first  apparent.  Besides  the  larger  species  of  animals  and  plants,  myriads  of  microscopic  forms  inhabit 
the  land,  the  water,  and  the  air.  From  the  burning  sands  of  tropical  deserts,  to  the  eternal  snows  of 
the  poles,  widely  differing  forms  occur,  each  being  peculiarly  fitted  for  its  own  conditions  of  growth. 

An  organic  form  differs  in  many  respects  from  one  that  is  inorganic.  The  animal  or  plant  has  its 
origin  in  a  germ ;  grows  from  nourishment  taken  into  its  structure ;  has  a  regular  development  in 
growth,  passing,  by  successive  stages,  from  birth  to  maturity,  when  it  reproduces  its  kind,  and  passes  on 
to  decay  and  death. 

A  crystal,  which  may  be  taken  as  the  type  of  the  inorganic  world,  grows  by  additions  from  without, 
does  not  reproduce  its  kind,  has  no  regular  development  or  growth,  being  perfect  from  its  first  existence, 
and  has  no  decay  or  death. 


Section  I. 


PLANT  LIFE. 


-oXKc 


CHAPTER   I. 
Plant  Geography. 

311.  Living  Matter. — All  life,  whether  vege- 
table or  animal,  consists  of  various  groupings  of 
118 


cells,  or  approximately  spherical  masses,  consist- 
ing of  a  peculiar  form  of  jelly-like  matter  called 
protoplasm,  composed  of  various  complex  combi- 
nations of  carbon,  hydrogen,  oxygen,  and  sulphur, 
called  proteids.  At  its  beginning  all  life  consists 
of  a  minute  germ  cell,  filled  with  more  or  less 


transparent  protoplasm,  and  containing  a  darker 
opaque  spot  called  the  nucleus.  Examined  by  a 
sufficiently  powerful  glass,  all  living  protoplasm 
is  seen  to  be  in  constant  motion,  currents  passing 
through  the  different  parts  in  somewhat  definite 
directions. 

As  the  germ  cell  develops,  in  all  the  higher 
forms  of  life,  it  multiplies,  and  various  organs 
appear,  peculiar  to  the  form  of  life  from  which 
the  germ  cell  was  derived.  All  living  bodies 
contain  organs,  and  living  matter  is  therefore 
sometimes  called  organic  matter,  to  distinguish  it 
from  non-living  or  inorganic  matter. 

Science  has  not  yet  disclosed  the  nature  of  the  change 
whereby  non-living  matter  is  converted  into  living  pro- 
toplasm. To  produce  living  matter  the  intervention  of 
already  living  matter  is,  so  far  as  is  known,  absolutely 
necessary. 

312.  Intermediate  Position  of  Plants. — Proto- 
plasm forms  an  essential  part  of  both  plants  and 
animals.  Plants  alone,  however,  possess  the  power 
of  manufacturing  protoplasm  directly  from  inor- 
ganic or  non-living  matter.  Plants  prepare  food 
for  animals,  who  are,  consequently,  dependent  on 
plants  for  their  existence.  Both  plants  and  ani- 
mals are  consumers  of  the  proteid  compounds. 
Plants  alone  are  producers.  In  the  scale  of  ex- 
istence plants,  therefore,  occupy  a  position  inter- 
mediate between  minerals  and  animals. 

313.  Plant  Geography  treats  of  the  distribu- 
tion of  plant-life  over  the  earth. 

Plant  geography  differs  essentially  from  botany.  Bot- 
any arranges  plants  into  regular  classes,  according  to  pe- 
culiarities in  their  organs  of  growth  and  reproduction. 
Plant  geography  considers  them  only  in  reference  either  to 
the  more  prominent  appearances,  by  which  they  give  a 
distinct  character  to  the  vegetation  of  a  country,  or  in 
regard  to  their  general  usefulness  to  man. 

In  this  limited  view,  all  the  minuter  differences  in 
structure  or  organization  are  passed  over,  the  general  form 
being  the  main  geographical  element  of  a  plant,  and  the 
element  with  which  physical  geography  is  principally  in- 
terested. 

The  plants  of  any  section  of  country,  taken 
collectively,  are  called  its  flora. 

314.  Conditions  Requisite  for  Plant  Growth. — 
Plants  require  for  their  growth  certain  conditions 
of  light,  heat,  and  moisture ;  and  since  the  requi- 
site amount  of  each  of  these  varies  with  different 
species  of  plants,  we  find  in  every  climatic  zone  a 
characteristic  flora.  The  soil  must  contain  those 
mineral  ingredients  which  form  a  part  of  the 
structure  of  the  plant,  and,  moreover,  must  con- 
tain them  in  a  condition  in  which  they  can  be 
readily  assimilated  by  the  plant. 


The  substance  of  plants  consists  mainly  of 
water  derived  from  the  air  and  the  soil.  Analy- 
sis shows  that  vegetable  matter  is  composed  almost 
entirely  of  water,  and  various  compounds  of  car- 
bon, hydrogen,  oxygen,  and  sulphur.  The  water 
is  derived  from  the  moisture  of  the  soil  and  of  the 
air ;  the  carbon,  from  the  carbonic  acid  of  the  air. 
The  exceedingly  small  proportion  of  mineral  mat- 
ter comes  directly  from  the  soil. 

The  nature  of  the  soil,  then,  is  far  from  being 
the  most  important  element  in  the  distribution  of 
mere  vegetation  ;  for,  even  when  a  soil  is  absent, 
if  the  other  requisites  of  light,  heat,  and  moist- 
ure are  present,  the  simpler  vegetable  forms  soon 
appear,  and  slowly  prepare,  even  on  a  bare, 
rocky  surface,  a  soil  which  is  able  to  sustain 
higher  and  still  higher  species.  This  is  effected 
by  the  breaking  up  of  the  hard  mineral  matter, 
and  the  accumulation,  year  after  year,  of  the  de- 
caying plants.  In  this  way  a  vegetable  mould  is 
produced.  The  bare  surfaces  which  the  conti- 
nents possessed,  when  they  first  emerged  from  the 
oceans,  gained  their  covering  of  soil  principally 
in  this  way. 

Moisture,  Heat,  and  Light  are  the  prime  essen- 
tials of  vegetation,  and  it  is  on  their  distribution 
that  the  distribution  of  vegetation  is  principally 
dependent. 

315.  Distribution  of  Vegetation. — The  influ- 
ence of  heat  and  moisture  is  noticed  as  we  pass 
from  the  equator  to  the  poles,  or  from  the  base 
of  a  tropical  mountain  to  the  summit.  Thus 
arises  a  horizontal  and  a  vertical  distribution  of 
vegetation. 

The  greatest  luxuriance  of  vegetation  is  found 
in  the  equatorial  regions,  where  both  heat  and 
moisture  are  most  abundant.  Here  a  greater  va- 
riety of  species  occurs,  and  the  individual  plants 
are  larger,  and  more  brilliantly  colored,  both  in 
their  leaves  and  flowers.  As  we  pass  toward  the 
poles,  the  number  of  the  species  diminishes;  trees 
disappear,  being  replaced  by  shrubs  and  herbs, 
and  these,  in  turn,  by  lichens  and  mosses,  until 
finally,  amid  the  snows  of  the  polar  latitude, 
even  the  simplest  forms  of  vegetable  life  are 
often  wanting. 

316.  Horizontal  Distribution  of  Vegetation. 

(1.)  According-  to  Meyen,  we  may  divide  the  earth's 
surface  into  zones  according  to  the  latitude,  and  the  moun- 
tainous elevations  into  zones  according  to  the  altitude. 
Since  the  distribution  of  heat  is  not  only  dependent  on 
the  latitude  or  altitude,  we  may  advantageously  modify 
this  plan  as  has  been  suggested  by  Dove,  and  divide  the 
zones  by  the  isotherms. 


120 


PHYSICAL    GEOGRAPHY. 


(2.)  According  to  Schouw,  we  may  divide  the  earth's 
surface  into  regions  characterized  by  assemblages  of  pecu- 
liar floras,  and  separated  by  natural  barriers. 

The  great  number  of  the  regions  required  to  give  thor- 
oughness to  Schouw's  system,  renders  its  use  inadvisable 
in  an  elementary  book. 

(3.)  According1  to  Humboldt  and  others,  we  may 
divide  the  earth's  surface  into  zones,  according  to  the 
physiognomy  of  the  plants  inhabiting  them.  Here  plants 
of  entirely  different  species  are  grouped  by  their  mere  out- 
ward resemblances  into  what  are  called  forms. 

The  first  method  is  the  one  most  suitable  for  our  pur- 
poses. We  shall  follow,  in  the  main,  Dove's  modification, 
as  adopted  by  A.  E.  Johnston,  and  divide  the  surface  of 
the  earth  into  zones,  according  to  the  isotherms,  or  lines 
of  mean  annual  temperature.  The  values  of  the  isotherms 
are  given  in  round  numbers.  This  system  is  based  on  the 
fact,  that  the  character  of  the  vegetation  is  dependent 
mainly  on  the  temperature,  which,  in  its  turn,  regulates 
the  quantity  of  moisture. 

317.  Horizontal  Zones  of  Vegetation. 

(1.)  The  Tropical  Zone,  extends  between  the 
isotherms  of  73°  Fahr.  on  each  side  of  the  equa- 
tor. 

(2.)  The  Sub-Tropical  Zones,  extend  in  each 
hemisphere  from  the  isotherm  of  73°  Fahr.  to  68° 
Fahr. 

(3.)  The  Warm  Temperate  Zones,  extend  in 
each  hemisphere  from  the  isotherm  of  68°  Fahr. 
to  55°  Fahr. 

(4.)  The  Cold  Temperate  Zones,  extend  in  each 
hemisphere  from  the  isotherm  of  55°  Fahr.  to  41° 
Fahr. 

(5.)  The  Sub- Arctic  Zone,  extends  in  the  north- 
ern hemisphere  from  the  isotherm  of  41°  Fahr. 
to  the  September  isotherm  of  36.5°  Fahr. 

(6.)  The  Polar  Zone,  extends  in  the  northern 
hemisphere  from  the  September  isotherm  of  36.5° 
Fahr.  to  the  poles. 

318.  The  Tropical  Zone,  or  the  zone  of  palms, 
bananas,  spices,  and  aromatic  plants,  lies  on  each 
side  of  the  equator,  between  the  isotherms  of  73° 
Fahr.  It  includes  most  of  the  land  within  the 
tropics  of  both  hemispheres. 

The  excessive  heat  and  moisture  of  this  zone 
produce  an  especial  luxuriance  in  the  vegetation. 
Trees  attain  enormous  size,  the  foliage  is  bright, 
the  flowers  brilliant,  and  the  number  of  species 
great.  The  forests  are  characterized  by  the  great 
variety  of  trees,  and  when  allowed  to  attain  their 
densest  growth,  are  almost  impenetrable,  from  the 
numerous  parasitic  plants  with  which  they  are 
covered*,  or  the  gigantic,  rope-like  climbers  that 
twine  among  them. 

Palms,  bananas,  tree-like  grasses,  and  orchids 
are  among  the  most  characteristic  plants. 


Orchids  are  curious  plants,   Inhabiting   damp  forests. 
They  attach  themselves  to  trees  and  rocks,  drawing  nearly 


^EtS  «*■ 


Fig,  104.    Palm-Trees. 


all  their  nourishment  from  the  air.  As  a  class,  they  are 
noted  for  the  fragrance,  vivid  coloring,  and  curious  forms 
of  their  flowers.  The  well-known  vanilla  bean  is  obtained 
from  an  orchid.  The  humble  grasses  of  our  latitude,  in 
this  zone,  are  represented  by  the  bamboo,  which  often  at- 
tains the  height  of  60  feet. 
The  banyan-tree,  a  species  of  fig-tree,  is  found  in  the 


Pig,  105.    Banyan -Tree. 

East  Indies.    From  a  colossal  trunk  numerous  air-branches 
are  sent  out,  which,  descending  to  the  ground,  take  root, 


122 


PHYSICAL    GEOGRAPHY. 


and  in  their  turn  send  out  other  branches,  and  in  this 
way  an  extended  area  is  covered.  A  single  tree  has  been 
known  sufficiently  large  to  give  shade  to  7000  men  at  the 
same  time. 

The  Llanos  of  the  Orinoco  are  found  in  the 
tropical  zone.  During  the  dry  season,  they  are 
almost  entirely  devoid  of  vegetation  ;  but  during 
the  wet  season,  they  are  covered  with  grasses. 

The  Indian  Archipelago  affords  an  excellent  illustration 
of  the  wonderful  luxuriance  of  the  vegetation  of  the 
tropics.  Here  the  gigantic  Eafflesia  bears  flowers  three 
feet  in  diameter! 

In  the  northern  and  southern  portions  of  the 
tropical  zone,  where  the  mean  annual  temperature 
ranges  from  79°  to  73°  Fahr.,  the  vegetation, 
though  similar  to  that  of  the  equatorial  regions, 
begins  to  lose  its  density  and  luxuriance.  The 
forests  contain  less  undergrowth  and  fewer  para- 
sitic plants.  Tree-like  ferns  and  figs  are  espe- 
cially abundant,  and  some  authorities  have  ar- 
ranged these  portions  into  separate  zones,  called 
the  zones  of  tree-ferns  and  figs. 

319.  The  Sub-Tropical  Zones,  or  the  Zones  of 
Laurels  and  Myrtles,  extend  in  each  hemisphere, 
from  the  isotherm  of  73°  Fahr.  to  68°  Fahr. 
Here,  the  heat  of  summer,  though  sufficient  to 
ripen  most  of  the  tropical  fruits,  is  not  as  intense 
as  in  the  tropical  zone.  The  winters  are  mild, 
and  scarcely  arrest  the  vegetation.  The  palms  and 
bananas  of  the  preceding  zones  are  still  common, 
but  the  characteristic  vegetation  is  found  in  the 
abundance  of  trees  with  thick,  shining  leaves,  such 
as  the  laurels,  magnolias,  and  myrtles. 

320.  The  Warm  Temperate  Zones,  or  the 
Zones  of  Evergreen  Trees,  or  trees  which  do  not 
shed  their  leaves,  extend  in  each  hemisphere, 
from  the  isotherm  of  68°  Fahr.  to  55°  Fahr.  In 
this  zone,  trees  with  thick,  shining  leaves  occur, 
mingled  with  oaks,  beeches,  and  others  similar  to 
those  found  in  our  own  forests.  No  palms  occur, 
but  in  their  place  we  find  a  number  of  glossy- 
leaved  evergreen  trees,  and  handsome  evergreen 
shrubs. 

In  those  portions  of  this  zone  which  are  in  the  neigh- 
borhood of  the  Mediterranean,  the  bay,  myrtle,  laurel,  fig, 
and  the  olive,  are  characteristic.  The  cork  oaks,  chest- 
nuts, and  pomegranates,  are  frequent.  The  vine,  said  to 
be  a  native  of  this  zone,  attains  here  its  greatest  growth, 
the  stem  often  reaching  a  thickness  of  half  a  foot.  In 
America,  oaks,  pines,  and  tulip-trees  occur. 

The  southern  warm  temperate  zone  includes 
portions  of  New  Zealand  and  Australia,  and  in 
South  America  the  Pampas  of  the  Rio  de  la 
Platte,  where  tree-like  grasses  abound. 


321.  The  Cold  Temperate  Zone,  or  the  Zone  of 
Deciduous  Trees,  or  those  which  drop  their  leaves 
in  autumn,  extends  in  the  northern  hemisphere, 
from  the  isotherm  of  55°  Fahr.  to  41°  Fahr.  For- 
ests of  deciduous  trees  are  the  main  characteristics 
of  this  zone ;  oaks,  birches,  beeches,  chestnuts,  wal- 
nuts, maples,  elms,  larches,  alders,  and  sycamores, 
are  among  the  most  common  of  the  deciduous 
trees.  Mosses  and  lichens  frequently  cover  the 
trunks  of  the  trees,  and  a  rich  and  varied  under- 
growth occurs ;  the  holly,  clematis,  wild  rose,  hon- 
eysuckle, and  rhododendron,  are  examples. 

Extensive  meadows,  covered  with  grasses,  are 
found  in  this  zone. 

The  deciduous  character  of  the  trees,  and  the  almost 
total  absence  of  evergreens,  produce  a  marked  contrast 
between  winter  and  summer.  During  winter,  the  foliage 
almost  entirely  disappears,  and  snow  covers  the  ground 
for  long  periods. 

This  zone  is  essentially  one  of  extensive  forests. 
In  connection  with  the  warm  temperate  zone  of 
the  northern  hemisphere,  it  has  always  contained 
the  most  highly  civilized  races  of  men,  and  is  es- 
pecially rich  in  the  number  and  luxuriance  of  its 
food-plants. 

322.  The  Sub-Arctic  Zone,  or  the  Zone  of  the 
Cone-Bearing  Trees,  extends  in  the  northern  hemi- 
sphere, from  the  isotherm  of  41°  Fahr.  to  regions 
where  the  mean  annual  temperature  for  the  month 


Fig,  106.    Pine-Trees. 

of  September  is  36.5°  Fahr.  In  this  zone,  both 
forests  and  grassy  meadows  abound.  The  forests 
are  especially  characterized  by  cone-bearing  trees, 
with  evergreen,  shining,  needle-shaped  leaves,  such 


PLANT    GEOGRAPHY. 


123 


as  the  pine,  spruce,  hemlock,  cedar,  and  fir.  In 
the  northern  portions  of  the  zone,  beeches  and 
alders  are  found,  and  willows,  when  the  soil  is 
moist.  The  meadows  are  covered  with  grasses 
and  flowers,  and  afford  abundant  pasturage. 

The  northern  limit  of  trees  is  marked  on  the  map  of 
the  plant  regions. 

323.  The  Polar  Zone,  or  the  Zone  of  Alpine 
Shrubs,  Mosses,  Lichens,  and  Saxifrages,  extends 
from  the  limits  of  the  sub-arctic  zone  to  the  pole. 
In  this  zone,  no  trees  occur  except  those  of  a  stunted 
growth.  Alpine  shrubs,  or  those  of  tortuous,  com- 
pact growth,  such  as  the  Alpine  rhododendra,  the 
dwarf  birch,  willow,  and  alder,  occur.  Sedges  and 
grasses  are  found.  The  pastures  of  the  preceding 
zones  are  absent ;  in  their  place  we  find  extended 
areas  covered  with  lichens. 

The  northern  plains  of  Siberia  are  covered  with  exten- 
sive marshes,  called  Tundras,  where  the  ground,  during 
most  of  the  year,  is  frozen  to  great  depths.  The  short 
summers  only  suffice  to  thaw  the  surface,  when  a  few 
mosses  and  lichens  appear. 


Near  the  extreme  northern  limits  of  the  North 
Polar  zone,  from  the  limit  of  the  isotherm  of  41° 
Fahr.  for  the  month  of  July,  such  plants  only  are 
found  as  can  thrive  during  the  brief  Arctic  sum- 
mer of  from  four  to  six  weeks.  Shrubs  are  en- 
tirely absent ;  lichens  and  mosses  occur,  together 
with  stunted  Alpine  herbs.  In  Spitzbergen,  lich- 
ens and  mosses  are  found,  the  former  being  espe- 
cially numerous. 

324.  The  Vertical  Distribution  of  Vegetation. — It 
is  difficult  to  make  a  good  systematic  arrangement  of  vege- 
tation into  vertical  zones,  since  the  temperature  and  moisture, 
on  which  such  an  arrangement  must  be  based,  are  subject 
to  very  considerable  variations.  Thus,  the  position  of  the 
mountain-ranges  as  regards  the  prevalent  wind,  the  direc- 
tion of  the  mountain  slopes,  and  the  extent  of  the  elevated 
plateaus,  all  exert  such  a  powerful  influence  on  the  mean 
annual  temperature  and  the  rainfall,  that  even  in  the 
same  range,  opposite  slopes,  or  even  different  parts  of  the 
same  slope,  afford  very  marked  climatic  contrasts.  In 
ranges  that  are  widely  separated,  the  differences  are  still 
greater.  The  following  chart  exhibits  the  characteristic 
flora  in  tropical  America,  Africa,  Europe,  and  Asia,  at 
similar  elevations. 


25,000  feet.    / 


20,000 


10,000 


5,000 


Fig.  107.    Vertical  Distribution  of  Vegetation.    (After  Black.) 


(1.)  Between  the  level  of  the  sea  and  5000  feet, 
the  vegetation  is,  in  general,  the  same  as  in  the  tropical 
and  sub-tropical  zones.  Palms,  bananas,  and  tree-ferns  oc- 
cur in  the  lower  parts,  and  barley,  potatoes,  sugar-cane, 
rice,  cotton,  etc.,  as  marked  on  the  chart. 

(2.)  Between  5000  and  10,000  feet,  the  vegetation 
is,  in  general,  the  same  as  in  warm  temperate  zones.  In 
America,  the  birch  and  cedar  occur  in  the  lower  portions 
of  the  region,  and  Peruvian  bark  and  the  cinchona  trees, 
so  useful  in  medicine,  in  the  upper  portions.  In  Africa 
and  Europe,  the  pine,  birch,  and  oak  occur;  and  in  Asia, 
the  oak ;  here  also  the  vine  is  cultivated. 

(3.)  Between  10,000  and  15,000  feet,  the  vegeta- 
tion, in  general,  is  that  of  the  cold  temperate  zones.  De- 
ciduous trees  occur ;  rye,  wheat,  barley,  and  oats  are  cul- 
tivated. 

(4.)  Between  15,000  and  20,000  feet,  the  flora  cor- 
responds, in  general,  to  that  of  the  polar  and  arctic  zones. 
A  few  rhododendrons  and  birches  occur  on  the  warmer 
Asiatic  slopes,  and  occasionally  crops  of  barley  are  culti- 


vated. The  greater  part  of  this  zone  is  covered  by  eternal 
snow,  as  is  the  case  with  all  greater  elevations. 

In  the  descriptions  here  given,  it  will  be  noticed  that 
the  correspondence  of  the  vertical  and  horizontal  zones  is 
but  of  a  very  general  character.  The  names  of  the  plants 
on  the  chart  mark  the  limits  at  which  they  will  grow. 

£.  325.  Plant  Regions. — In  some  localities,  a  few 
plants  occur  over  extended  areas,  in  such  vast 
numbers  as  to  give  a  characteristic  appearance  to 
the  country  they  cover.  A  brief  mention  will  be 
made  of  such  regions,  especially  as  they  illustrate 
the  influence  of  the  presence  or  absence  of  moist- 
ure on  the  vegetation. 

326.  Forests  occur  wherever  the  moisture  is 
abundantly  and  regularly  distributed  throughout 
the  year.  As  a  rule,  forests  are  limited  to  those 
portions  of  the  world  where  the  rain  falls  at  all 


124 


PHYSICAL    GEOGRAPHY. 


times  of  the  year,  or  is  abundant  during  the  sea- 
son the  tree  is  growing,  as  in  the  zones  of  the 
variable  winds.  Forests  may  also  occur  in  por- 
tions of  the  tropics  where  moisture  is  abundant. 

The  forests  of  the  cold  temperate  zones  are  de- 
ciduous; those  of  the  other  zones,  evergreen. 

327.  Steppes. — When  the  moisture  is  not  well 
distributed  throughout  the  year,  but  the  rainfall 
is  periodical,  and  long  droughts  occur  in  the  in- 
tervals between  the  rainy  seasons,  the  forests  are 
replaced  by  areas  called  steppes,  which,  during 
the  wet  seasons,  are  covered  with  grasses,  shrubs, 
or  herbs ;  but  during  the  dry  seasons  are  almost 
destitute  of  vegetation.  Steppes  are  found  in  the 
Llanos  and  Pampas  in  South  America,  in  the 
Great  Plains  of  North  America,  in  the  grassy 
steppes  of  Australia,  Russia,  and  Asia,  in  the 
German  heaths,  and  in  the  African  savannas. 

328.  Meadows  and  Prairies. — These,  like  the 
preceding,  are  covered  with  tall  grasses,  but  the 
vegetation  is  more  permanent,  the  droughts  being 
only  occasional.  They  are  found,  therefore,  in  the 
temperate  zones,  in  the  regions  of  constant  rains. 
An  extended  prairie  region  is  found  in  the  valley 
of  the  Mississippi,  on  both  sides  of  the  stream. 


Pig.  108.    Desert  Scene. 

329.  Deserts  are  regions  characterized  by  an 
almost  entire  absence  of  vegetation ;  they  are 
found  mainly  in  the  zones  of  the  trade  winds, 
and  are  to  be  ascribed  entirely  to  the  absence 
of  moisture.  Their  bare  surfaces  are  subject  to 
great  and  sudden  changes  of  temperature,  being, 
as  a  rule,  excessively  warm  during  the  day,  and 
often   quite   cool  at  night.     These   changes  are 


due  to  the  readiness  with  which  a  bare  surface 
receives  and  parts  with  heat. 


CHAPTER  II. 

Cultivated  Plants. 

330.  Plants  appear  to  have  been  originally 
confined,  by  conditions  of  soil  or  climate,  to  cer- 
tain localities.  In  many  instances,  however,  plants 
furnishing  materials  for  food,  clothing,  or  other 
staples  for  the  human  family,  have  been  trans- 
planted and  widely  diffused  by  man.  In  most  of 
these  cases,  their  successful  cultivation  is  limited 
to  regions  where  suitable  climate  and  soil  ex- 
isted either  naturally,  or  have  been  artificially 
produced. 

331.  Distribution  of  the  Cereals. — The  cereals 
include  barley,  rye,  oats,  wheat,  maize  or  Indian 
corn,  and  buckwheat ;  together  with  the  potato, 
they  form  the  more  important  food-plants  of  the 
temperate  zones. 

Barley,  thought  to  be  a  native  of  Tartary  and 
Sicily,  can  be  grown  farther  north  than  any  other 
grain ;  in  Lapland,  as  far  as  70°  N.  lat. 

Rye  is  found  as  far  north  as  lat.  67°  N.  in  Nor- 
way. It  is  the  most  common  grain  in  Russia, 
Germany,  and  in  portions  of  France. 

Oats  is  probably  a  native  of  the  Caucasus ;  its 
northern  limit  in  Norway  is  about  65°  N.  lat. 


Fig.  109.    Maize,  or  Indian  Corn. 


Wheat  is  probably  a  native  of  Tartary.     It  is 
the  most  important  of  the  cereals,  and  has  a  wide 


CULTIVATED    PLANTS. 


125 


vertical  and  horizontal  distribution.  Its  northern 
limit,  in  Norway,  is  64°  N.  lat. 

Maize,  or  Indian  Corn,  a  native  of  America,  is 
extensively  cultivated  from  the  southern  part  of 
Chili  to  high  latitudes  in  North  America.  Its 
northern  European  limit  is  perhaps  near  the  iso- 
therm of  65°  Fahr. 

Buckwheat,  probably  a  native  of  the  colder 
portions  of  the  Chinese  Empire,  is  extensively 
cultivated  in  Siberia,  on  the  plateaus  of  Central 
Asia,  and  generally  in  the  cool  temperate  regions 
of  the  rest  of  the  world.  Buckwheat  is  especially 
valuable  on  account  of  the  ability  it  possesses  of 
thriving  in  sandy  or  moory  soils,  where  other 
similar  food-plants  will  not  succeed. 

Potatoes. — The  native  country  of  the  potato 
appears  to  have  been  either  Chili  or  Peru. 
Though  cultivated  in  both  the  tropical  and  tem- 
perate regions,  it  is  to  be  regarded  as  a  food- 
plant  of  the  temperate  zones.  It  possesses  a  very 
remarkable  range,  being  cultivated  from  the  ex- 
tremity of  Africa  to  Lapland :  the  requisite  cold 
in  the  tropical  regions  being  found  on  mountain- 
slopes. 

332.  The  Food-Plants  of  the  Tropical  Regions, 

are  rice,  dates,  cocoa-nuts,  bananas  and  plantains, 
cassava,  bread-fruit,  sago,  yams,  etc. 

Rice  is  cultivated  in  tropical  Africa,  Egypt, 
Nubia,  Persia,  China,  the  Americas,  and  the  West 
Indies.  It  requires  considerable  heat  and  an 
abundance  of  moisture.  Puce  forms  the  main 
food  of  a  large  portion  of  the  world. 

Dates  form  an  important  article  of  food  in 
North  Africa,  both  for  man  and  beast.  Dates 
are  obtained  from  the  date-palm,  a  native  of  a 
strip  of  land  on  the  southern  slopes  of  the  Atlas 
Mountains,  where  the  tree  occurs  so  plentifully  as 
to  give  to  the  country  the  name  of  Beled-el-Jerid, 
or  the  Land  of  Dates.  Different  varieties  of  the 
date  are  found  in  the  Saharan  oases,  and  in  other 
parts  of  the  world. 

Cocoa-nuts  are  the  product  of  the  cocoa-palm, 
which  is  valuable  for  its  food,  timber,  foliage,  and 
fibres.  The  cocoa-palm  is  a  native  of  Southern 
Asia,  but  is  cultivated  throughout  the  tropical 
regions  of  Ceylon,  Sumatra,  Java,  and  the  islands 
of  Polynesia. 

Bananas  and  Plantains  are  thought  to  be  na- 
tives of  Southern  Asia.  They  are  extensively 
cultivated  throughout  the  tropical  zones,  both 
north  and  south  of  the  equator.  Since  their 
fruit  is  very  nutritious,  and  the  yield  of  a  given 
15 


area  great,  they  form  an  exceedingly  important 
staple  of  food. 


Fig.  110.    Banana. 

Cassava  is  obtained  from  the  manioc,  a  shrub 
with  a  fleshy  root,  several  feet  long,  and  nearly 
as  thick  as  a  man's  arm.  Tapioca  is  one  of  the 
varieties  of  cassava.  Some  species  of  the  man- 
ioc are  poisonous,  when  raw,  but  become  edible 
when  cooked.  The  manioc  is  a  native  of  Brazil, 
but  is  abundantly  cultivated  in  Western  Africa, 
in  Congo  and  in  Guinea. 


Fig.  111.    Bread-Fruit. 

Bread-Fruit  is  the  pulpy  fruit  of  a  tree  which 
grows  only  in  the  tropics.  The  fruit,  when  baked, 
resembles  potato  bread  in  taste.     The  tree  yields 


126 


PHYSICAL    GEOGRAPHY. 


fruit  during  most  of  the  year,  and  is  said  to  be  a 
native  of  the  South  Sea  Islands,  though  it  is  now 
quite  common  in  the  Friendly  and  Society  groups, 
and  in  many  of  the  neighboring  islands. 

Sago  is  a  starchy  substance,  obtained  from  the 
pith  of  several  species  of  palm  trees,  which  grow 
in  the  Moluccas.  A  single  tree  is  said  to  yield 
from  600  to  800  pounds  of  sago. 

Yams  are  the  large  tubers  of  a  number  of 
plants,  resembling  potatoes.  They  are  cultivated 
in  Africa,  in  South  America,  and  in  Cuba. 

333..  Sugar-Cane  is  probably 
a  native  of  India,  but  is  now 
extensively  cultivated  through- 
out the  tropical  and  warm  tem- 
perate zones  of  both  hemispheres, 
in  the  West  Indies  and  South- 
ern United  States,  Guinea  and 
Brazil,  Mauritius  and  Bourbon, 
Bengal,  Siam,  China,  Java,  and 
the  neighboring  islands. 

334.  Fruits  of  the  Tropical 
and  Warm  Temperate  Zones. — 
Besides  those  already  enumer- 
ated, we  find  the  following: 
oranges,  lemons,  limes,  citrons, 
pine- apple  s, 
f\.  \    \  mangoes,  figs ; 

and  in  the 
cooler  por- 
tions cherries, 
peaches,  apri- 
cots, andjoome- 
granates. 

335.  Distri- 
bution  of 
Plants  yield- 
ing Bever- 
ages.— The 
principal  plants  yielding  beverages  by  infusion 
are  tea,  coffee,  and  cocoa. 

Tea  consists  of  the  dried  leaves  of  a  number 
of  evergreen  shrubs,  natives  of  China  or  there- 
abouts. Tea  is  cultivated  in  China  and  India, 
from  the  equator  as  far  north  as  lat.  45°.  It  ap- 
pears to  thrive  best  between  25°  and  33°  N.  lat. 
It  is  extensively  cultivated  in  Malacca,  Java,  and 
in  various  portions  of  the  English  possessions  in 
India.  '  Tea  was  introduced  into  Europe  by  the 
Dutch,  in  1610. 

Coffee  is  the  berry  of  a  tree  found  native  in 
Abyssinia.     The  tree  attains  a  height  of  from 


Fig.  112.    Sugar-Oane. 


15  to  20  feet,  but  when  cultivated,  it  is  generally 
kept  lower  by  cutting.      The   tree   has  shining 


Fig,  113,    Tea-Plant. 

green  leaves,  and  bears  beautiful  white  flowers, 
which  are  followed  by  reddish-brown  berries,  each 
of  which  contains  two  grains  of  coffee.  The 
coffee-tree  is  cultivated  extensively  in  Arabia, 
Java,  the  Philippines,  Ceylon,  Brazil,  and  in  the 
West  Indies. 


Fig.  114.    Coffee. 

Cocoa. — The  cocoa-tree  is  cultivated  in  Central 
America,  Guiana,  Chili,  India,  Japan,  and  in 
several  islands  in  the  Indian  Ocean.  The  tree 
attains  a  height  of  about  20  feet.  Chocolate  is 
prepared  from  the  seed  of  the  cocoa-tree. 

336.  Spices,  such  as  pepper,  cloves,  nutmegs,  and 
cinnamon,  are  cultivated  mainly  within  the  trop- 
ics. Vanilla,  used  in  flavoring,  is  also  limited  to 
this  region. 

Pepper. — The  black  pepper  of  commerce  is  ob- 
tained from  the  dried  seed  of  a  climbing  shrub, 
which  grows  wild  on  the  western  coasts  of  Hin- 


SYLLABUS. 


127 


dostan.  Red,  or  Cayenne  pepper,  is  grown  in 
Guiana  and  the  East. 

Cloves  are  the  dried  flower-buds  of  an  ever- 
green tree,  thirty  or  forty  feet  high,  which  grows 
in  the  Moluccas.  The  cultivation  of  the  tree  is 
confined  mainly  to  the  little  island  of  Amboyna. 

Nutmegs. — The  tree  from  which  nutmegs  are 
obtained  is  found  mainly  on  the  Banda  Islands, 
south  of  Ceram.  The  nutmeg  is  covered  by 
several  layers  of  vegetable  matter,  one  of  which 
is  the  mace  of  commerce. 

Cinnamon  is  the  inner  bark  of  a  tree,  which  is 
cultivated  mainly  on  the  island  of  Ceylon. 

Vanilla  is  obtained  from  the  dried,  fragrant 
pods  of  a  plant  grown  mainly  in  Mexico,  Cen- 
tral America,  and  Brazil. 

337.  The  Principal  Narcotics  used  in  different 
countries  are  opium,  prepared  from  a  species  of 
poppy ;  the  betel-plant,  a  native  of  Hindostan : 
the  leaves  of  the  betel-plant  are  chewed,  together 
with  the  areca-nut ;  hasheesh,  a  narcotic  used  in 
India ;  and  tobacco,  the  dried  leaves  of  a  plant 
grown  extensively  in  Mexico,  Cuba,  Brazil,  and 
in  the  United  States. 

338.  Plants  Valuable  as  giving  Materials  for 
Clothing,  are  cotton,  hemp,  and  flax /^ 

Cotton,  a  native  of  India,  is  now  grown  exten- 


sively in  East  India,  Persia,  on  the  eastern  shores 
of  the  Mediterranean,  in  various  parts  of  Europe, 
and  in  North  and  South  America. 

Hemp  and  Flax  are  cultivated  in  the  temper- 
ate regions  of  Russia,  and  throughout  Great 
Britain  and  the  United  States. 

The  plants  producing  medicines,  and  products 
employed  in  the  arts  or  manufactures,  are : 

The  Cinchona-Tree,  found  on  the  upper  slopes 
of  the  tropical  Andes.  Quinine  is  obtained  from 
the  bark  of  the  tree. 

Gum  Arabic,  obtained  from  the  East  Indies, 
Egypt,  and  Africa. 

Indigo,  a  blue  dye,  obtained  from  the  indigo- 
bearing  plants. 

Brazil-Wood,  Nicaragua-Wood,  and  Log-Wood, 
yield  reddish  dyes. 

Quercitron  and  Slack  Oak,  yield  a  yellow  dye. 

Turpentine  and  Rosin,  are  products  of  the  pine 
tree. 

Caoutchouc,  or  India-rubber,  is  the  juice  of 
several  tropical  plants. 

Olive  Oil  is  derived  from  the  olive-tree,  culti- 
vated on  the  borders  of  the  Mediterranean. 

Cocoa-nut,  Palm,  Flaxseed  and  Cotton-Seed 
Oils,  are  obtained  respectively  from  the  cocoa- 
nut,  palm-tree,  and  the  seeds  of  flax  and  cotton. 


SYLLABUS. 


All  life  consists  of  groupings  of  cells  or  spherical  masses, 
consisting  of  a  transparent  jelly-like  substance  called  pro- 
toplasm. 

All  life  originates  in  a  germ  cell  produced  through  the 
agency  of  pre-existing  life. 

Protoplasm  forms  an  essential  part  of  all  plants  and  ani- 
mals. Both  plants  and  animals  consume  protoplasm  dur- 
ing their  growth.  Plants,  alone,  produce  protoplasm.  Ani- 
mals are  dependent  on  plants  for  their  existence. 

Plants  require  for  their  vigorous  growth  certain  condi- 
tions of  light,  heat,  moisture,  and  soil;  of  these,  heat  and 
moisture  are  the  most  important. 

Plant  geography  treats  of  the  distribution  of  plants.  It 
differs  essentially  from  botany,  which  treats  of  the  pecu- 
liarities in  the  structure  of  plants. 

The  plants  of  any  section  of  country,  taken  collectively, 
are  called  its  flora. 

The  differences  in  the  distribution  of  heat  and  moisture, 
produce  corresponding  differences  in  the  distribution  of 
vegetation.  The  distribution  of  heat  and  moisture,  there- 
fore, forms  the  true  basis  for  the  distribution  of  plant  life. 

If  a  soil  be  wanting  in  any  section  of  country,  but  the 
proper  conditions  of  light,  heat,  and  moisture  be  present, 


the  simpler  vegetable  forms  will  appear,  and  gradually 
prepare  a  soil  fitted  for  the  higher  kinds  of  vegetation. 

The  variety  and  luxuriance  of  vegetation  decrease  as 
we  pass  from  the  base  to  the  summit  of  a  mountain,  or 
from  the  equator  to  the  poles;  this  decrease  is  caused 
by  a  corresponding  decrease  in  the  amount  of  heat  and 
moisture. 

According  to  the  horizontal  distribution  of  plants,  the 
surface  of  the  earth  is  divided  into  the  following  zones : 
the  tropical,  sub-tropical,  warm  temperate,  cold  temper- 
ate, sub-arctic,  and  polar. 

The  tropical  zone  is  characterized  by  the  prevalence  of 
palms,  bananas,  spices,  and  aromatic  plants. 

The  sub-tropical  zones  are  characterized  by  the  preva- 
lence of  laurels,  myrtles,  and  magnolias. 

The  tropical  and  sub-tropical  zones,  especially  the 
former,  are  particularly  characterized  by  an  especial 
luxuriance  of  their  vegetation. 

The  warm  temperate  zones  are  characterized  by  forests 
of  evergreen  trees. 

The  cold  temperate  zones  are  characterized  by  forests 
of  deciduous  trees. 

Deciduous  trees  are  those  which  cast  their  leaves  in 


128 


PHYSICAL    GEOGRAPHY. 


autumn.  Oaks,  birches,  beeches,  chestnuts,  walnuts,  ma- 
ples, elms,  larches,  alders,  and  sycamores  are  among  the 
most  common  of  the  deciduous  trees. 

Extensive  grass-covered  meadows  are  found  in  the  cold 
temperate  plant  zones. 

The  sub-arctic  zone  is  characterized  by  cone-bearing 
trees.    The  polar  zone,  by  Alpine  shrubs  and  mosses. 

Forests  require,  for  their  luxuriant  growth,  an  abun- 
dance of  moisture,  evenly  distributed  throughout  the 
year,  or  during  the  time  the  trees  are  growing. 

Steppes  are  regions  covered  with  a  scanty  vegetation ; 
they  are  produced  either  by  insufficient  moisture,  or  its 
irregular  distribution  throughout  the  year. 


The  principal  cereals  are  barley,  rye,  oats,  wheat,  maize, 
corn,  and  buckwheat. 

The  principal  food-plants  of  the  tropical  regions  are 
rice,  dates,  cocoa-nuts,  bananas,  plantains,  cassava,  sago, 
yams,  and  bread-fruit. 

Some  of  the  most  important  plants  cultivated  for  the 
beverages  they  yield,  are  tea,  coffee,  and  cocoa. 

The  principal  spices  are  pepper,  cloves,  nutmegs,  and 
cinnamon.  The  principal  narcotics  are  opium,  betel, 
hasheesh,  and  tobacco. 

Cotton,  hemp,  and  flax  are  valuable  as  furnishing  mate- 
rials for  clothing. 

The  cinchona-tree  yields  quinine. 


REVIEW   QUESTIONS. 


What  is  protoplasm  ?    Of  what  does  all  life  consist? 

In  what  respect  are  animals  dependent  upon  plants  for 
their  existence  ? 

Define  plant  geography.  In  what  respect  does  it  differ 
from  botany?  Name  the  conditions  requisite  for  plant 
growth. 

How  do  these  conditions  compare  with  each  other  in 
importance  ?    Describe  the  formation  of  soil. 

Why  is  soil  of  comparatively  less  importance  to  the  ex- 
istence of  vegetation  than  heat  or  moisture  ? 

What  do  you  understand  by  the  horizontal  distribution 
of  vegetation  ?    By  the  vertical  distribution  ? 

What  is  the  main  cause  of  the  difference  in  the  flora  of 
different  parts  of  the  world  ? 

Why  should  the  isothermal  lines  generally  form  the 
boundaries  of  the  plant  zones? 

Name  the  horizontal  zones  of  vegetation. 

State  the  boundaries  of  each  of  these  zones. 

What  is  the  characteristic  flora  of  the  tropical  zone  ? 

Why  should  the  vegetation  of  the  tropics  be  so  much 
more  luxuriant  than  that  of  the  rest  of  the  world? 

Why  should  the  same  change  be  noticed  in  the  vegeta- 
tion of  a  high  tropical  mountain,  in  passing  from  its  base 
to  its  summit,  as  in  passing  along  the  earth's  surface  from 
the  equator  to  the  poles  ? 

Describe  the  vertical  vegetable  zones.  To  what  hori- 
zontal zone  does  each  of  these  correspond? 

Name  the  conditions  requisite  for  the  luxuriant  growth 


of  forests.  How  do  the  forests  of  the  cold  temperate  zones 
differ  from  those  of  other  zones? 

By  what  climatic  conditions  are  steppes  produced? 

What  conditions  are  requisite  for  the  production  of 
meadows  and  prairies?    How  are  deserts  produced? 

Name  some  of  the  more  important  cereals. 

Which  of  the  cereals  form  the  principal  food-plants  of 
the  temperate  zones  ?  Which  of  the  cereals  has  the  far- 
thest northern  range?    Which  is  the  most  important? 

Name  the  principal  food-plants  of  the  tropical  regions. 

What  is  the  principal  region  for  the  cultivation  of 
dates?  Name  the  principal  regions  in  the  world  noted 
for  the  successful  cultivation  of  the  sugar-cane. 

Name  the  fruits  of  the  tropical  and  warm  temperate  zones. 

In  what  portions  of  the  world  is  coffee  successfully  cul- 
tivated ?    Where  is  tea  cultivated  ? 

From  what  tree  is  chocolate  obtained? 

From  what  plant  is  black  pepper  obtained  ?  Where  is 
the  plant  cultivated? 

From  what  are  cloves  obtained  ?  Where  is  the  tree  cul- 
tivated ?    Where  are  nutmegs  grown  ?    What  is  mace  ? 

In  what  part  of  the  world  is  cinnamon  cultivated? 

Name  the  principal  narcotics  used  in  different  parts  of 
the  world. 

Name  the  plants  which  furnish  valuable  materials  for 
clothing. 

From  what  tree  is  quinine  obtained  ? 

Name  some  of  the  principal  vegetable  dyes. 


MAP  QUESTIONS. 


-»o>»4c 


Trace  on  the  map  showing  the  distribution  of  vegeta- 
tion, the  parts  of  the  world  included  in  the  tropical 
zone. 

Name  the  plants  of  the  tropical  zone  which  are  charac- 
teristic of  South  America.  Name  those  of  Africa.  Of 
India  and  Australia. 

Describe  the  principal  region  of  the  cocoa-nut  palm, 
bread-fruit,  sago,  and  yam  in  the  eastern  continent. 

Describe  from  the  map  the  limits  of  the  sub-tropical 
zones.  Describe  the  characteristic  flora  of  those  por- 
tions of  each  of  the  continents  which  lie  within  these 
zones. 

Describe  the  limits  of  the  warm  temperate  zones.    Of 


the  cold  temperate  zones.  Of  the  sub-arctic  zone.  Of  the 
polar  zone. 

Trace  on  the  map  the  northern  limit  of  trees.  Trace 
the  southern  limit  of  trees. 

Name  some  of  the  trees  of  the  warm  temperate  zones. 
Of  the  cold  temperate  zones.     Of  the  sub-arctic  zones. 

In  what  parts  of  the  world  are  pasture-lands  found  ? 

Name  the  characteristic  plants  of  the  regions  which  lie 
north  of  the  arctic  circle. 

Trace  on  the  map  showing  the  vertical  distribution  of 
vegetation,  the  characteristic  plants  found  in  Africa,  be- 
tween the  level  of  the  sea  and  5000  feet.  In  Europe.  In 
Asia.    In  America. 


ZOOLOGICAL    GEOGRAPHY. 


129 


Section  II. 


ANIMAL    LIFE. 


CHAPTER   I. 
Zoological  Geography. 

339.  Zoological  Geography  treats  of  the  dis- 
tribution of  animal  life.  The  animals  found  in 
any  region  of  country  are  called  its  fauna.  Like 
plants,  animals  appear  to  have  been  originally 
created  in  certain  localities,  from  which  they  have 
spread,  more  or  less,  over  adjoining  areas. 

Though  able  to  move  about  freely  from  place 
to  place,  animals  are,  nevertheless,  restricted,  by 
conditions  of  food  and  climate,  to  well-defined 
areas.  Animals  derive  their  sustenance,  either 
directly  or  indirectly,  from  plants. 

340.  Distribution  of  Animal  Life. — The  distri- 
bution of  heat,  moisture,  and  vegetation  forms  the 
true  basis  for  the  distribution  of  animal  life. 

We  distinguish  a  horizontal  and  a  vertical  dis- 
tribution of  animal  life. 


25,000  feet. 
20,000    " 
15,000    " 
10,000    " 
5,000      " 


As  a  rule,  the  luxuriance  and  diversity  of  ter* 
restrial  animal  life  decrease  as  we  pass  from  the 
equator  to  the  poles.  A  similar  decrease  is  no- 
ticed in  passing  from  the  coasts  of  the  continents 
toward  the  interior.  Within  the  tropics,  where 
the  abundant  heat  and  moisture  produce  a  vigor- 
ous vegetation,  all  forms  of  terrestrial  animal  life, 
save  man,  attain  the  greatest  development  in  size, 
intelligence,  and  activity.  As  we  proceed  toward 
the  poles,  the  species  are  less  developed,  although, 
in  the  temperate  regions,  large  and  vigorous  ani- 
mals are  still  numerous.  In  the  polar  zones,  the 
reindeer  and  white  bear  are  the  only  representa- 
tives of  the  larger  land  animals. 

In  marine  animal  life,  the  law  of  distribution 
is  reversed,  both  the  number  and  size  of  the 
species  increasing  from  the  equator  toward  the 
poles.  This  is  probably  due  to  the  more  equable 
temperature  of  the  ocean  in  high  latitudes. 

341.  The  Vertical  Distribution  of  Life. — In 


Ta^sjsak 


Fig.  115.    Vertical  Distribution  of  Animal  Life.    (After  Black.) 


passing  from  the  base  to  the  summit  of  a  tropical 
mountain,  the  same  change  is  noticed  in  the  spe- 
cies of  animals,  as  in  passing  along  the  surface  of 
the  earth  from  the  equator  to  the  poles. 

In  the  above  chart,  the  names  of  the  animals 
are  placed  at  the  greatest  elevation  at  which  they 
are  found.  The  power  of  locomotion  possessed  by 
animals  renders  it  extremely  difficult  to  arrange 
the  fauna  in  zones  according  to  the  altitude.     In 


general,  however,  the  animals  found  on  the  slopes 
of  tropical  mountains,  at  elevations  included  be- 
tween the  sea-level  and  from  5000  to  7000  feet, 
correspond  to  those  inhabiting  the  tropical  zone ; 
between  5000  or  7000  feet  and  15,000  feet,  to 
those  of  the  temperate  zones.  The  condor  is 
found  in  the  high  Andes,  far  above  the  snow 
line. 
The  fauna  of  high  mountain-ranges  are  often  sharply 


130 


PHYSICAL    GEOGRAPHY. 


marked.  A  particular  species,  at  a  given  elevation  on  one 
range,  is  frequently  entirely  wanting  on  a  neighboring 
disconnected  range,  even  when  the  same  conditions  of 
heat,  moisture,  and  vegetation  exist.  The  temperature 
of  the  intervening  lower  country,  through  which  the  ani- 
mals would  have  to  pass  in  order  to  reach  the  adjoining 
slopes,  forms  an  impenetrable  barrier. 

342.  Natural  Boundaries  of  Zones  of  Animal 
Life. — Large  bodies  of  water,  deserts,  or  moun- 
tain-ranges, mark  the  boundaries  of  regions  of 
animals  as  well  as  of  plants ;  but  the  influence 
of  temperature  is  so  important,  that  even  when 
these  natural  barriers  are  wanting,  the  horizontal 
range  of  animals  is  sharply  marked  by  the  iso- 
thermal lines. 

In  North  America,  there  are  well-marked  zones  of  ani- 
mals, which  extend  from  east  to  west  across  the  continent. 
Here,  although  no  natural  barriers  exist  to  limit  the  wider 
range  of  the  animals,  yet  they  seem  unable  to  permanently 
pass  the  limits  of  the  isotherms,  which  mark  the  climatic 
conditions  necessary  to  their  vigorous  growth.  This  in- 
ability doubtless  arises  from  the  distribution  of  the  flora, 
on  which,  directly  or  indirectly,  they  are  dependent  for 
their  food. 

343.  Acclimation. — The  power  of  becoming 
acclimated,  or  being  able  to  live  in  a  climate  dif- 
fering from  that  in  which  they  were  first  created, 
appears  to  be  possessed  by  animals,  as  a  class,  to 
an  exceedingly  limited  extent. 

Man,  and  his  faithful  friend,  the  dog,  form  an  exception 
to  most  other  animals  in  this  respect.  They  are  able  to 
endure  both  the  severe  heat  of  the  tropics,  and  the  rigor 
of  the  Arctic  regions.  The  reindeer  thrives  amid  the 
snows  of  Lapland  or  Greenland,  but  perishes  from  the 
heat  of  St.  Petersburg.  Monkeys  are  indigenous  to  the 
tropics,  but  die  with  consumption,  even  in  the  compara- 
tively mild  climate  of  the  north  temperate  zones. 

344.  Horizontal  Distribution  of  Animal  Life. 

— The  vast  number  of  species  of  animals,  the  pe- 
culiar laws  of  their  growth,  and  their  power  of 
adaptation  to  change  of  circumstances,  render 
their  accurate  distribution  into  zones  or  regions 
a  task  far  beyond  the  scope  of  an  elementary 
book.  It  will  be  sufficient  for  our  purpose  to 
divide  the  fauna  of  the  earth  into  those  found,  in 
general,  in  the  three  mathematical  climatic  zones : 
the  Torrid,  the  Temperate,  and  the  Polar.  The 
accurate  limits  of  these  zones  would  be  found  in 
the  isotherms,  but  in  a  general  description,  little 
difference  would  be  noticed.  On  the  map,  the 
actual  limits  of  some  of  the  more  important  ani- 
mals are  given.  These  limits,  it  will  be  noticed, 
in  most  cases  follow  the  general  direction  of  the 
isotherms. 

345.  Characteristic  Fauna. — A  careful  study 


of  the  map  of  the  distribution  of  animal  life,  will 
show  that  each  continent  possesses  a  fauna  pecu- 
liar to  itself.  This  arises,  generally,  from  some 
clearly  traceable  peculiarity  in  the  distribution 
of  the  heat  and  moisture,  or  in  the  nature  of  the 
vegetation.  Some  of  these  peculiarities  will  be 
discussed  in  a  brief  review  of  the  characteristic 
fauna  of  each  of  the  continents.  The  following 
are  the  characteristic  tropical,  temperate,  and  arc- 
tic fauna. 

346.  Tropical  Fauna.  —  The  abundance  of 
heat,  moisture,  and  vegetation  of  the  torrid 
zone  causes  its  fauna  to  excel  all  the  others 
in  the  number  and  diversity  of  terrestrial 
species,  as  well  as  in  their  size,  strength,  and 
sagacity. 

The  following  animals  are  found  mainly  within 
the  regions  of  the  earth  included  between  the 
Tropics  of  Cancer  and  Capricorn. 

Mammalia  are  represented  as  follows : 

Monkeys,  by  the  man-like  orang-outang,  the 
chimpanzee,  gorilla,  baboon,  and  other  species. 


Tig.  116.    Lion, 

Carnivora,  or  flesh-eating  mammals,  by  the  lion, 
tiger,  panther,  and  puma. 

Herbivora,  or  plant-eating  mammals,  by  the  ele~ 
phant,  rhinoceros,  tapir,  and  hippopotamus,  the 
horse-like  zebra  and  quagga,  the  giraffe  or  camel- 
opard,  and  the  camel. 

Cetacea,  or  whales,  by  the  sperm  whale,  found 
only  in  tropical  or  temperate  waters. 

Cheiroptera,  or  bats,  by  a  number  of  species. 

Marsupials,  by  the  kangaroo  of  Australia. 

Birds  are  represented,  in  tropical  regions,  by 


Page  131. 


132 


PHYSICAL    GEOGRAPHY. 


species  noted  for  their  great  size  and  strength,  or 
for  the  brilliant  colors  of  their  plumage.  Among 
those  noted  for  their  size  may  be  mentioned  the 
condor,  ostrich,  eagle,  ibis,  flamingo,  and  cassowary ; 
among  those  especially  noted  for  their  plumage, 
the  birds  of  paradise,  peacock,  and  parrots,  and 
the  humming-birds  of  South  America,  which  lat- 
ter, though  in  less  brilliantly-colored  plumage, 
extend  nearly  to  the  extreme  limits  of  the  north 
and  south  temperate  zones. 


Fig.  117.    Alligator. 

Reptiles  are  represented  by  the  crocodile,  alli- 
gator, iguana,  gigantic  lizards,  and  turtles  ;  among 
serpents,  the  enormous  boa-constrictor,  and  num- 
bers of  hooded  and  other  venomous  serpents. 

The  Fish  of  tropical  waters,  though  large  and 
brightly  colored,  are  not  so  well  adapted  for  food 
as  the  more  sombre  varieties  of  the  temperate  or 
colder  waters. 
\*^  347.  Temperate  Fauna. — The  following  ani- 
mals are  found  mainly  between  the  tropics  and 
polar  circles.  Though  fewer  of  the  higher  spe- 
cies of  animals  are  found  in  the  temperate  zone 
than  in  the  torrid  zone,  yet  many  of  the  fauna 
are  of  large  size,  and  among  them  are  found  ani- 
mals most  useful  to  man. 

The  physical  tropical  zone,  as  will  be  seen  from  an  in- 
spection of  the  map  of  plant  life,  actually  extends,  in  the 
eastern  continent,  far  into  the  mathematical  north  tem- 
perate zone,  and  in  these  portions  the  corresponding  trop- 
ical species  occur.  Thus,  in  Northern  Africa  and  South- 
ern Asia,  are  found  the  ape,  tiger,  lion,  panther,  camel,  and 
rhinoceros. 

Mammalia  are  represented  as  follows : 
Flesh-eating  mammals,  by  the  lynx,  hyena,  wolf, 
jackal,  dog,  fox,  raccoon,  bear,  seal,  and  walrus. 
Plant-eating  mammals,  by  the  wild  boar  and  hog, 


the  horse,  ass,  ox,  sheep,  goat,  and  chamois,  many 
of  which  have  been  domesticated,  as  the  moose, 
elk,  reindeer,  stag,  antelope,  buffalo,  camel,  llama, 
and  numerous  others. 

Cetacea,  or  whales,  by  the  sperm  and  white 
whales. 

Rodentia,  or  gnawing  mammals,  by  the  beavers, 
squirrels,  rats,  and  porcupines. 

Marsupials,  by  the  kangaroo  of  Australia. 

The  birds  of  the  temperate  zones  are  repre- 
sented  by  the  condor,  vulture,  hawk,  eagle,  owl, 


Fig.  118.    Eagles. 

and  parrot  (near  the  southern  limit  of  the  zone). 
The  turkey,  pheasant,  and  our  common  domesti- 
cated fowls  also  are  natives  of  this  zone.  Here 
occur  numerous  birds  which  are  noted  for  the 
sweetness  of  their  song,  as  the  wren,  thrush,  robin, 
nightingale,  and  lark;  the  pelican,  albatross,  and 
the  cassowary  are  found  in  this  zone. 

Reptiles  are  represented  by  the  alligator,  croco- 
dile, and  lizard,  and  the  rattlesnake,  copperhead, 
and  various  other  serpents,  both  poisonous  and 
harmless. 

348.  Arctic  Fauna. — The  following  animals 
are  found  mainly  between  the  polar  circles  and 
the  poles.  The  south  arctic  fauna  is  but  little 
known ;  the  following  description,  therefore,  re- 
fers mainly  to  the  northern  hemisphere: 

In  the  arctic  regions  of  the  world,  the  large 
land  animals  are,  with  a  few  exceptions,  replaced 
by  numerous  smaller  furry  species.     Throughout 


CHARACTERISTIC    FAUNA    OF    THE    CONTINENTS. 


13< 


the  northern  portions  of  the  north  temperate 
zone,  and  the  southern  portions  of  the  arctic, 
fur-bearing  animals  are  especially  numerous  and 
valuable. 

The  white  polar  bear,  the  reindeer,  moose,  and 
the  musk-ox,  are  among  the  largest  of  the  land 
species ;  but  in  warmer  regions  of  the  oceans,  nu- 
merous species  exist,  among  which  are  individuals 
as  large  as  any  in  the  animal  world. 

The  Greenland  whale,  which  sometimes  attains  the  length 
of  seventy  feet,  and  is  covered  with  blubber  to  a  thick- 
ness of  two  or  three  feet,  is  found  only  in  this  zone.  A 
similar,  though  smaller,  species  occurs  in  the  southern 
waters.    The  seal  and  walrus  are  also  found  in  this  zone. 


Fig,  119,    Seals  and  Walrus. 

Besides  the  larger  animals,  numerous  smaller 
species,  such  as  minute  zoophytes,  mollusks,  and 
crustaceans,  which  form  the  food  of  the  whale, 
and  which,  in  some  places,  exist  in  immense 
numbers,  inhabit  the  waters.  Among  birds,  in- 
numerable water-fowl  occur. 


3^0^0-f 


CHAPTER  II. 

Characteristic  Fauna  of  the  Conti- 
nents. 

349.  Characteristic  Fauna  of  the  Continents. 

— Each  of  the  continents  is  characterized  by  some 
peculiarity  in  its  fauna.  This  peculiarity  arises 
either  from  the  nature  of  the  vegetation,  or  the 
distribution  of  the  heat  and  moisture,  and  affords 


an  excellent  example  of  the  intimate  connection 
between  the  physical  features  of  a  country,  and 
its  flora  and  fauna.  Only  the  general  character- 
istics of  the  fauna  will  be  given. 

For  the  particular  animals  inhabiting  each  continent, 
the  student  is  referred  to  the  map  of  the  distribution  of 
animal  life. 

350.  North  American  Fauna. — The  chief  cha- 
racteristic of  the  North  American  fauna  is  found 
in  the  preponderance  of  plant-eating  mammals. 
This  feature  is  due  to  the  abundance  of  pasture- 
lands,  and  their  luxuriant  vegetation.  From  its 
extensive  lake  and  river  systems,  North  America 
is  peculiarly  fitted  to  sustain  aquatic  life ;  hence, 
its  numerous  water-fowl  and  beaver. 

351.  Fur-bearing  animals  are  particularly  nu- 
merous and  valuable.  Three  natural  districts  of 
fur-bearing  animals  exist :  the  forest  region,  the 
prairie  region,  and  the  barren  regions  of  the 
north,  each  of  which  is  characterized  by  a  pecu- 
liar fauna. 

Forest  Region  — Here,  among  carnivora,  are  found  the 
black  bear,  marten,  ermine,  mink,  otter,  the  silver  fox,  the  black 
fox,  and  the  lynx;  among  the  rodentia,  the  beaver  and 
musk-rat ;  and  among  the  ruminants,  the  moose  and  rein- 
deer. The  wolverine  and  wolf  are  found  both  in  the  for- 
est region  and  the  barren  grounds. 

Barren  Grounds. — The  brown  and  polar  bears,  the  polar 
fox,  and  the  polar  hare  are  characteristic. 

Prairie  Region. — The  grizzly  bear,  the  most  formidable 
animal  of  the  continent ;  the  prairie  wolf,  and  the  gray  fox 
are  also  found  here. 

The  puma,  or  the  American  lion,  which  is  found 
also  over  the  greater  part  of  South  America,  is 
the  most  powerful  representative  of  the  lion  and 
tiger  tribe  of  the  East. 

352.  South  American  Fauna. — The  chief  cha- 
racteristics of  the  South  American  fauna  arise 
from  the  extreme  luxuriance  of  its  vegetation, 
due  to  the  abundance  of  its  moisture.  In  vast 
districts,  as  the  Selvas  of  the  Amazon,  the  vege- 
table world  usurps  the  ground  nearly  to  the  ex- 
clusion of  the  higher  forms  of  animal  life.  The 
fauna  is,  therefore,  as  a  rule,  characterized  by  its 
fitness  for  existing  in  connection  with  either  an 
abundance  of  water  or  of  vegetation. 

Insect  Life  is  peculiarly  characteristic  of  the 
continent.  Nowhere  else  are  the  species  so  nu- 
merous, so  brilliantly  colored,  or  so  large.  Here 
are  found  the  largest  of  the  beetles,  and  the  most 
beautiful  of  the  butterflies. 

Reptiles  are  largely  represented.  They  find, 
in  the  tepid,  sluggish  waters  of  the  huge  rivers, 
conditions  most  favorable  to  rapid  growth.    Here 


134 


PHYSICAL    GEOGRAPHY. 


live  the  crocodile,  gigantic  lizards,  and  many 
venomous  serpents. 

Among  Birds,  the  water  species  are  in  the  as- 
cendance. Humming-birds,  which  occur  also  in 
North  America,  are  found  in  great  abundance  in 
the  southern  continent.  The  condor  is  found  on 
the  higher  slopes  throughout  the  Andes ;  the  os- 
trich, toucan,  and  parrot  are  also  characteristic. 

Among  the  Mammalia,  the  ant-eaters  and  sloths 
peculiarly  characterize  the  continent.  The  tapir 
and  peccary  are  the  only  representatives  of  the 
elephant,  rhinoceros,  and  hippopotamus  of  the 
Eastern  continents.  The  llama,  puma,  and  the 
prehensile-tailed  monkeys  are  also  characteristic 
of  the  region. 

The  South  American  district  of  fur-bearing  animals  ex- 
tends through  parts  of  Chili  and  the  Argentine  Eepublic. 
The  marsh  heaver  is  the  principal  animal. 

353.  Asiatic  Fauna. — From  the  great  mass  of 
land  within  the  tropics,  the  fauna  of  Asia,  besides 
its  numerous  arctic  and  temperate  species,  contains 
a  great  variety  of  tropical  forms. 

Taken  in  connection  with  Northern  Africa, 
Asia  is  essentially  the  region  of  extensive  dry 
plains  and  arid  tracts.     The  vegetation  through- 


Fig.  120.   Elephant. 

out  its  temperate  climes  is  greatly  inferior  to  that 
of  America,  but  its  animal  life  is  marked  by  a 
much  greater  variety  in  the  higher  forms.     Fore- 


most among  these  are  the  man-like  monkeys,  the 
orang-outang,  the  elephant,  the  royal  tiger,  and 
others,  fur-bearing  animals  are  also  numerous. 
Among  birds,  those  with  bright,  gay-colored 
plumage  abound.  Reptiles  also  are  repre- 
sented, though  not  to  such  an  extent  as  in 
South  America. 

When  we  bear  in  mind  that  in  Asia,  the  horse, 
ass,  goat,  sheep,  camel,  swine,  elephant,  buffalo, 
and  ox  are  found  in  great  numbers,  it  will  be 
seen  that  Asia,  the  home  of  primitive  man,  is 
also  peculiarly  the  home  of  domesticated  animals; 
that  is,  of  the  animals  which  man  has  trained  to 
labor  for  him. 

The  Asiatic  district  of  fur-bearing  animals  includes  Si- 
beria, Kamtchatka,  and  the  basin  of  the  Amoor  River  in 
Mantchooria.  The  following  animals  are  characteristic: 
the  brown  bear,  badger,  weasel,  ermine,  sable,  otter,  marten, 
and  many  others.  The  furs  of  the  sable,  black  fox,  otter, 
and  the  ermine,  are  considered  the  most  valuable. 

354.  African  Fauna. — The  peculiarities  of  the 
northern  portion  of  the  continent  have  been  al- 
ready pointed  out  in  connection  with  Asia.  It  is 
a  fact  worthy  of  notice,  that  the  great  deserts  of 
the  world,  like  the  Sahara,  though  nearly  desti- 
tute of  any  vegetation,  are  able  to  sustain  many 
of  the  highest  species  of  animals. 

Over  these  tracts  are  found  the  lordly  lion,  the 
leopard,  and  the  panther,  and  the  numerous  ani- 
mals on  which  they  prey,  such  as  the  antelope, 
the  zebra,  the  quagga,  and  others.  All  these 
possess  powers  of  rapid  locomotion,  which  pe- 
culiarly fit  them  for  the  arid  plains  over  which 
they  roam. 

In  the  remaining  portions  of  Africa,  the  luxu- 
riant vegetation  is  capable  of  sustaining  animals 
of  a  larger  growth.  Here  occur  the  largest  of 
the  Mammalia,  such  as  the  elephant,  rhinoceros, 
and  hippopotamus ;  here  also  is  found  the  giraffe, 
the  largest  of  the  ruminantia ;  man-like  monkeys 
are  also  characteristic. 

355.  Australian  Fauna. — The  more  nearly  per- 
fect isolation  of  Australia  than  any  of  the  other 
continents,  together  with  the  peculiar  distribu- 
tion of  its  heat  and  moisture,  causes  its  fauna 
and  flora  to  differ  markedly  from  those  of  all 
the  other  continents. 

Australia  is  essentially  the  home  of  the  marsu- 
pials. These  are  both  carnivorous  and  herbivor- 
ous. The  kangaroo  is,  perhaps,  the  most  cha- 
racteristic of  the  marsupials.  Large  and  power- 
ful animals  are  entirely  absent;  in  this  respect 
the  continent  offers  a  sharp  contrast  to  Africa. 


DISTRIBUTION    OF    THE  HUMAN    RACE. 


135 


The  birds  are  also  of  peculiar  species,  such  as  the 
emu,  cassowary,  dodo,  and  apterix. 


o&ic 


CHAPTER   III. 


The  Distribution  of  the 
Race. 


Human 


356.  Ethnography  is  that  department  of  phys- 
ical geography  which  treats  of  the  varieties  of 
the  human  race,  and  their  distribution. 

The  range  of  the  distribution  of  man  is  much 
greater  than  that  of  the  lower  animals,  which,  as 
we  have  already  seen,  with  the  trifling  exception 
of  a  few  that  have  been  domesticated,  are  confined 
to  certain  limited  localities.  Man  has  far  greater 
powers  of  adapting  himself  to  a  change  of  cir- 
cumstances, and  is  found  in  nearly  all  the  climatic 
zones,  from  the  equator  to  the  poles,  and  at  all 
elevations,  from  the  level  of  the  sea  to  the  edge 
of  the  snow  line. 

357.  Unity  of  the  Human  Race. — Although 
the  different  races  of  men  vary  greatly  in  color, 
size,  stature,  and  intelligence,  still  a  number  of 
circumstances  point  to  their  descent  from  a  single 
family  or  species. 

(1.)  The  Anatomical  Structure  is  invariably 
the  same  in  all  races. 

(2.)  Gradual  Modification  of  Types  presented 
by  the  different  races.  The  more  marked  out- 
ward peculiarities,  which  serve  as  the  basis  for 
classification,  pass  into  each  other,  by  almost  in- 
sensible gradations,  from  the  highest  race  to  the 
lowest.  This  points  to  a  gradual  modification  of 
a  single,  original  race  by  changes  in  external  cir- 
cumstances, thus  producing  the  present  varieties. 
It  would  appear  that  all  the  varieties  of  the  race 
have  descended  from  the  Caucasians,  or  whites. 

(3.)  Similarity  of  Earlier  Myths  and  Legends. 
Since  the  earlier  myths  and  legends  of  nearly  all 
nations  resemble  each  other,  it  is  fair  to  infer  that 
their  remote  ancestors  originally  dwelt  together. 

(4.)  Close  Resemblance  of  Language  of  Widely 
Separated  Races.  This  may  be  regarded  as  the 
strongest  proof  of  unity. 

If  we  examine  the  words  used  in  different  na- 
tions to  express  the  most  common  ideas,  we  will 
find  a  remarkable  similarity  between  many  of 
them.  For  example,  our  word  father  is  pita  in 
Sanscrit,  pater  in  Latin,  pater  in  Greek,  voter  in 
German,  and  pere  in  French.     The  same  similar- 


ity is  noticeable  in  the  words  for  mother,  sister, 
brother,  daughter,  God,  and  many  others.  The 
only  rational  explanation  for  the  resemblance  is, 
that  the  words  were  derived  from  the  same  parent 
language,  the  present  differences  having  been 
gradually  acquired,  as  the  descendants  of  this 
earlier  people  wandered  farther  and  farther  from 
their  common  home. 

An  extended  comparison  made  in  this  way  between  dif- 
ferent languages,  has  shown  the  common  origin  of  the  lan- 
guages of  Europe  and  a  large  part  of  Asia.  It  has  been 
conclusively  proved  that  these  tongues  owe  their  origin 
to  one  parent  nation,  which  dwelt,  during  pre-historic  times, 
in  the  neighborhood  of  Mt.  Ararat  and  Mesopotamia. 

Other  families  of  languages,  such  as  the  Chinese  and 
Semitic,  have  been  studied,  but  thus  far  the  connection 
between  the  different  families  has  not  been  certainly  es- 
tablished. 


NEGRO.  MONGOLIAN. 

Fig.  121.    Primary  Races  of  Men, 

358.  The  Races  of  Men. — Among  the  varieties 
of  +he  human  race,  three  strongly-marked  types 
are  found :  the  Caucasian,  the  Mongolian,  and 
the  Negro.  These,  which  may  be  regarded  as  the 
primary  races,  are  grouped  around  three  geograph- 
ical centres,  which  correspond  nearly  to  the  cen- 
tres of  the  three  divisions  of  the  Old  World. 

The  Caucasian  type  is  found  in  most  of  Europe 
and  in  South-western  Asia ;  the  Mongolian  type, 
in  those  parts  of  Europe  and  Asia  not  occupied 
by  the  Caucasian ;  the  Negro  type,  in  Africa. 
The  other  parts  of  the  world  are  peopled  mainly 
by  three  other  races,  which,  in  general,  bear  close 
resemblances  to  the  preceding.  These  are  the 
Malay,  the  American,  and  the  Australian.     They 


Page  136. 


DISTRIBUTION    OF    THE    HUMAN    RACE. 


137 


are  called  the  secondary  races,  and  appear  to  be 
modifications  of  the  Mongolian. 

359.  Cranial  Characteristics. — The  primary  races  are 
sharply  distinguished  by  the  following  types  of  skull : 

Caucasian.  The  skull  is  nearly  oval,  and  the  arch  of 
the  cheek-bones  moderate. 

Mongolian.  The  skull  is  nearly  round,  the  occipito- 
frontal diameter,  or  the  distance  from  the  forehead  to  the 
back  of  the  head,  is  slightly  greater  than  the  parietal 
diameter,  or  that  between  the  temples. 

Negro.  The  skull  is  elongated  from  the  back  of  the 
head  to  the  forehead ;  that  is,  the  occipitofrontal  diam- 
eter greatly  exceeds  the  parietal.  The  cheek-bones  are 
large  and  projecting. 

360.  The  Caucasian,  or  White  Race  is  charac- 
terized by  a  round  or  oval  head ;  symmetrical 
features ;  vertical  teeth ;  round  or  oval  face ; 
arched  forehead ;  fair  complexion,  and  ample 
beard. 

The  Caucasian  race  inhabits  South-western 
Asia  (Hindostan,  Persia,  and  Arabia),  Northern 
Africa,  and  nearly  the  whole  of  Europe.  The 
descendants  of  the  race  now  people  large  portions 
of  America,  Australia,  and  Southern  Africa. 

361.  Divisions  of  the  Caucasian  Race. — The 
Caucasian  race  may  be  divided  into  three  branches : 
the  Hamitic,  the  Semitic,  and  the  Japhetic. 

(1.)  The  Hamitic  Races  originally  inhabited 
Palestine,  the  shores  of  the  Arabian  Peninsula, 
and  the  valley  of  the  Nile.  They  are  now,  how- 
ever, scarcely  distinguishable  from  the  other 
branches  of  the  Caucasian  race,  with  whom  they 
have  intermarried. 

(2.)  The  Semitic,  or  Syro-Arabian  Races,  com- 
prise the  modern  Syrians,  the  Jews  or  Hebrews, 
the  inhabitants  of  Arabia  and  Abyssinia,  and  the 
greater  part  of  Northern  Africa. 

Among  the  ancient  peoples  belonging  to  this  branch  of 
the  Caucasian  race,  are  the  Assyrians  and  Babylonians, 
the  Israelites,  Moabites,  Ammonites,  Edomites,  Ishmael- 
ites,  and  Phoenicians. 

(3.)  The  Indo- Europeans,  or  the  Aryan  Race, 
comprise  the  Japhetic  race.  They  are  the  most 
civilized  peoples  of  the  world,  and  include  the 
following  nations: 

(1.)  Celtic  Nations,  including  the  Irish,  Welsh,  Scots,  and 
the  Bretons  of  France. 

(2.)  Romanic  Nations,  comprising  the  Italians,  Spaniards, 
Portuguese,  and  the  French. 

(3.)  The  ancient  Greeks. 

(4.)  Germanic  Nations,  comprising  the  Germans,  Anglo- 
Saxons  (English),  Dutch,  Flemish,  Danes,  Swedes,  and  the 
Norwegians. 

(5.)  Slavonic  Nations,  comprising  the  Russians,  Poles, 
Croats,  and  Czechs. 

(6.)  Nations  of  the  Iranian  Plateau,  comprising  the  Per- 
sians, Belooches,  and  the  Afghans. 

(7.)   The  Hindoos. 
16 


362.  The  Mongolian,  or  Yellow  Race.— The 
chief  characteristics  of  the  Mongolian  race  are : 
broad  head ;  angular  face ;  high  cheek-bones ; 
small,  obliquely-set  eyes ;  straight,  coarse,  black 
hair ;  scanty  beard,  and  short  stature.  The  color 
of  the  skin  varies  from  pale  lemon  to  brownish 
yellow. 

The  Mongolian  race  includes  the  inhabitants 
of  all  of  Asia,  except  a  small  part  of  the  Malay 
Peninsula,  and  those  portions  of  the  continent 
occupied  by  the  Caucasians.  It  also  includes  the 
Lapps  and  Finns,  inhabiting  the  northern  por- 
tions of  Europe,  the  Turks  of  Europe,  and  the 
Magyars  of  Hungary,  In  America,  the  race  is 
represented  by  the  Esquimaux,  who  inhabit 
Greenland  and  the  northern  borders  of  the 
North  American  continent. 

In  Central  Asia,  the  race  is  represented  by  the  Thibetans, 
Chinese,  Indo-Chinese,  and  others. 

In  Northern  Asia,  by  the  Samoides,  inhabiting  the  shores 
of  the  Arctic  Ocean,  from  the  Petchora  to  the  Yenisei,  and 
south  to  the  Altai  Mountains ;  the  Ugrian,  or  Finnic  races, 
inhabiting  the  upper  valley  of  the  Obe,  and  a  part  of 
Northern  Europe ;  the  Tchooktchees,  the  Tungusians,  and 
the  Yakuts,  of  North-eastern  Asia. 

Other  branches  of  the  race,  are  the  Coreans,  Japanese, 
Kamtchatdales,  Koriaks,  and  the  Mongols. 

363.  The  Negro,  or  Black  Race—  The  chief 
characteristics  of  this  race  are :  narrow  and  elon- 
gated head ;  crisp  and  curly  hair ;  projecting 
jaws;  thick  lips;  soft  and  silky  skin;  color  black 
or  dusky ;  scanty  beard,  especially  on  upper  lip ; 
broad  feet,  and  projecting  heel-bones. 

The  race  inhabits  the  entire  continent  of 
Africa,  excepting  those  parts  occupied  by  the 
Caucasians. 

The  following  are  the  most  important  varieties  of  the 
race :  the  Jaloffs,  Mandingoes,  and  Ashantis,  in  the  west- 
ern part ;  the  Tibboos,  in  the  north  central ;  the  Gallas, 
in  the  eastern ;  the  Congo  Negroes,  in  the  south  central ; 
and  the  Hottentots  and  Kaffirs,  in  the  extreme  south. 

The  Negro  tribes  differ  greatly  in  their  civili- 
zation :  the  Gallas,  though  cruel  and  vindictive, 
are  a  handsome,  gifted  race ;  the  Hottentots,  on 
the  contrary,  are  among  the  most  debased  creat- 
ures in  existence. 

364.  The  Secondary  Races. — The  Malay,  or 
Brown  Race;  the  Australian;  and  the  American, 
or  Copper-colored  Race,  are  modifications  of  the 
Mongolian  Race. 

365.  The  Malay,  or  Brown  Race. — The  princi- 
pal characteristics  of  this  race  are  the  same  as 
those  which  distinguish  the  Mongolian  ;  the  eyes, 
however,  are  horizontal,  the  face  flat,  and  the  hair 


138 


PHYSICAL    GEOGRAPHY. 


less  coarse  and  straight.  The  color  of  the  skin 
varies  from  a  clear  brown  to  a  dark  olive.  In 
the  Papuans,  it  is  dark  brown,  and  even  black. 


AUSTRALIAN. 

Fig.  122. 


AMERICAN  INDIAN. 

Races  of  Men. 


This  race  inhabits  the  southern  part  of  the 
Malay  Peninsula,  the  island  of  Madagascar,  and 
the  islands  of  the  Indian  and  Pacific  Oceans. 

The  different  peoples  included  under  the  Malay 
race  present  the  most  strongly  marked  contrasts. 
The  Papuans,  for  example,  differ  widely  in  their 
appearance  from  the  normal  Malay.     They  are, 


perhaps,  allied  more  closely  to  the  Aiistralians 
than  to  any  others. 

366.  The  Australian  Race  is  to  be  regarded  as 
a  sub-variety  of  the  Papuan  branch  of  the  Ma- 
lays. It  inhabits  all  the  continent  of  Australia 
not  settled  by  the  whites. 

The  Australian  race  possesses  the  following 
characteristics :  the  head  is  large ;  eyes  deep-set ; 
nose  broad ;  hair  dark ;  beard  abundant.  The 
color  of  the  skin  varies  from  dark  brown  to  deep 
black.  The  Australians  are  almost  wholly  desti- 
tute of  civilization. 

367.  The  American,  or  Copper-colored  Race, 
though  containing  many  widely  differing  varie- 
ties, yet  possesses,  in  some  respects,  many  com- 
mon features.  Its  general  resemblance  to  the 
Mongolian  is  evident,  but  the  top  of  the  skull  is 
more  rounded,  and  the  sides  less  angular.  This 
race,  though  once  numerous  and  powerful,  is  now 
rapidly  disappearing  before  the  whites. 

In  Lower  California,  Mexico,  Peru,  and  Bra- 
zil, the  old  races  have  become  mixed  with  Span- 
ish and  other  elements. 

The  ruins  of  temples,  and  once  populous  cities,  are  com- 
mon on  the  high  Andean  plateaus.  These  parts  of  the 
earth  were  inhabited  at  the  time  of  the  discovery  of  the 
continent  by  a  people  who  had  made  considerable  progress 
in  the  art  of  working  metals,  and  who  were  probably  of 
Asiatic  origin. 

The  plateaus  of  Central  America  contain  the  traces  of  a 
still  higher,  though  more  ancient  civilization,  the  origin 
of  which  is  unknown,  though  some  trace  it  to  a  Semitic 
or  an  Egyptian  source. 


SYLLABUS. 


The  animals  of  any  section  of  country  are  called  its 
fauna. 

Notwithstanding  their  powers  of  locomotion,  animals 
are  restricted,  by  conditions  of  food  and  climate,  to  well- 
defined  areas. 

Since  animals  are  dependent  for  their  existence  upon 
plants,  the  heat  and  moisture  of  any  given  section  of 
country  form  the  true  basis  for  the  distribution  of  its 
fauna. 

We  distinguish  a  horizontal  and  vertical  distribution 
of  animal  life. 

The  same  change  is  noticed,  in  the  species  of  animals, 
in  passing  from  the  base  to  the  summit  of  high  tropical 
mountains,  as  in  passing  along  the  surface  of  the  earth 
from  the  equator  to  the  poles. 

Terrestrial  animal  life  attains  its  greatest  development, 
both  as  regards  luxuriance  and  diversity, .  within  the 
tropics. 


Marine  animal  life  attains  its  greatest  development  in 
the  colder  waters  of  the  polar  regions  and  vicinity. 

Man  attains  his  greatest  mental  development  in  the 
temperate  zone. 

As  regards  the  vertical  distribution  of  life,  the  fauna  of 
regions  between  the  sea  level  and  5000  or  7000  feet,  resem- 
bles, in  general,  that  of  the  tropics ;  between  the  preced- 
ing and  15,000  feet,  that  of  the  temperate  zones. 

The  boundaries  of  animal  regions  are,  in  general,  to  be 
found  in  the  isothermal  lines. 

As  a  class,  animals  appear  to  possess  to  but  a  limited  de- 
gree the  power  of  living  in  a  climate  differing  greatly 
from  that  in  which  they  were  first  created. 

The  fauna  of  the  earth  may  be  conveniently  arranged 
under  three  heads:  the  tropical,  temperate,  and  arctic. 

The  tropical  fauna  are  characterized  by  the  number  and 
diversity  of  terrestrial  species,  as  well  as  their  size, 
strength,  and  sagacity. 


KEVIEW    QUESTIONS. 


139 


In  tropical  fauna,  the  mammalia  are  represented  as  fol- 
lows: 

Monkeys,  by  the  orang-outang,  chimpanzee,  gorilla,  and 
baboon. 

Flesh-eating  mammals,  by  the  lion,  tiger,  panther,  and 
puma. 

Plant-eating  mammals,  by  the  elephant,  rhinoceros,  ta- 
pir, hippopotamus,  zebra,  quagga,  giraffe,  and  camel. 

Marsupials,  by  the  kangaroo. 

Birds  are  represented  by  the  condor,  ostrich,  eagle,  ibis, 
flamingo,  cassowary,  bird  of  paradise,  peacock,  and  parrot. 

Reptiles,  by  the  crocodile,  alligator,  iguana,  and  turtles. 

The  temperate  fauna,  though  characterized  by  fewer  of 
the  higher  species  of  animals,  yet  contain  many  of  large 
size,  and  among  them  animals  of  great  use  to  man. 

In  temperate  fauna,  the  carnivorous  mammalia  are  rep- 
resented by  the  lynx,  hyena,  wolf,  jackal,  dog,  fox,  rac- 
coon, bear,  seal,  and  walrus. 

The  herbivorous  mammalia,  by  the  wild  boar,  hog, 
horse,  ass,  ox,  sheep,  goat,  chamois,  moose,  elk,  reindeer, 
stag,  antelope,  buffalo,  camel,  and  llama. 

The  gnawing  mammals,  by  the  beaver,  squirrel,  rat,  and 
porcupine. 

The  whale,  by  the  sperm  and  white  whale. 

The  marsupials,  by  the  kangaroo. 

Birds,  by  the  condor,  vulture,  hawk,  eagle,  owl,  parrot, 
turkey,  pheasant,  wren,  thrush,  robin,  nightingale,  lark, 
pelican,  and  albatross. 

The  arctic  fauna  contain  but  comparatively  few  large 
land  species;  the  chief  characteristics  are  numerous 
smaller  furry  species. 

In  the  marine  arctic  fauna  numerous  species  are  found, 
some  of  which,  as  the  whale,  are  among  the  largest  in  the 
animal  world. 

The  terrestrial  arctic  fauna  are  characterized  by  the  fol- 
lowing animals:  the  white  polar  bear,  the  reindeer,  the 
moose,  and  the  musk-ox. 

The  marine  fauna,  by  the  Greenland  whale,  the  seal, 
and  the  walrus. 

The  peculiar  distribution  of  the  vegetation  of  the  con- 
tinents produces  corresponding  peculiarities  in  their  cha- 
racteristic fauna. 

The  North  American  continent  is  characterized  by  the 
preponderance  of  its  plant-eating  mammals.  The  cause 
of  this  peculiarity  is  to  be  found  in  the  abundance  of  its 
pasture  lands. 

Fur-bearing  animals  particularly  characterize  the  north- 
ern and  central  portions  of  North  America. 

There  are  three  natural  districts  of  fur-bearing  animals 
in  North  America:  1.  The  forest  region;  2.  The  barren 
grounds;  3.  The  prairie  regions. 

The  South  American  continent  is  especially  character- 
ized by  the  predominance  of  reptilian  life,  aquatic  birds, 


and  insects.  The  cause  of  the  peculiarity  is  traceable  to 
the  predominance  of  the  vegetable  life  over  the  animal. 

The  Asiatic  continent  is  especially  characterized  as 
being  the  original  home  of  most  of  the  animals  which 
man  has  domesticated.  The  cause  of  this  peculiarity  is 
traceable  to  the  fact  that  Asia  was  the  primitive  home  of 
man  himself. 

The  great  deserts  of  Africa  are  characterized  by  the 
presence  of  animals  which  are  peculiarly  noted  for  their 
swiftness  of  locomotion. 

In  the  remaining  portions  of  Africa,  the  luxuriant  vege- 
tation sustains  animals  of  a  larger,  bulkier  growth;  as,  for 
example,  the  elephant,  rhinoceros,  hippopotamus,  and  the 
giraffe. 

Australia  is  peculiarly  characterized  by  the  presence  of 
the  marsupials.  It  is  the  home  of  the  kangaroo,  the  most 
important  of  the  marsupials. 

Ethnography  treats  of  the  varieties  of  the  human  race, 
and  their  distribution. 

Man  has  a  wider  range  of  distribution  than  any  other 
animal. 

It  is  believed  by  most  that  all  the  varieties  of  the  hu- 
man race  were  originally  descended  from  one  family. 

Though  greatly  different  in  color,  size,  stature,  and  in- 
telligence, the  general  anatomical  structure,  the  basis  on 
which  all  other  animals  are  classified,  is  invariably  the 
same,  even  in  the  most  widely  differing  races. 

The  languages  of  Europe  and  of  a  large  portion  of  Asia, 
appear  to  owe  their  origin  to  one  parent  nation,  which 
dwelt,  during  pre-historic  time,  in  the  neighborhood  of 
Mount  Ararat  and  Mesopotamia. 

The  primary  races  are  the  Caucasian,  the  Mongolian, 
and  the  Negro. 

The  secondary  races  are  modifications  of  the  Mongolian : 
they  are  the  Malay,  the  American,  and  the  Australian. 

The  Caucasian  race  inhabits  South-western  Asia,  North- 
ern Africa,  and  nearly  the  whole  of  Europe. 

The  Caucasian  race  may  be  divided  into  three  branches : 
the  Hamitic,  the  Semitic,  and  the  Japhetic,  or  the  Indo- 
Europeaus. 

The  Mongolian  race  inhabits  all  of  Asia,  except  a  small 
part  of  the  Malay  Peninsula  and  those  portions  of  the 
continent  occupied  by  the  Caucasians. 

The  Chinese,  Japanese,  Esquimaux,  Lapps,  Finns,  Turks, 
and  Magyars,  are  among  the  most  important  of  the  Mon- 
golians. 

The  Negro  race  inhabits  all  the  continent  of  Africa  not 
occupied  by  the  Caucasians. 

The  Malay  race  inhabits  the  southern  part  of  the  Malay 
Peninsula,  Madagascar,  and  the  islands  of  the  Indian  and 
Pacific  Oceans. 

The  Australian  race  inhabits  all  the  continent  of  Aus- 
tralia not  settled  by  the  whites. 


REVIEW   QUESTIONS. 


►oJ*Kc 


Define  zoological  geography.    Fauna. 

Why  should  the  distribution  of  heat  and  moisture  form 
the  true  basis  for  the  distribution  of  animal  life? 

Distinguish  between  the  horizontal  and  the  vertical  dis- 
tribution of  animals. 

What  difference  exists  between  terrestrial  tropical  fauna 
and  marine  tropical  fauna  ? 

Between  what  limits,  in  the  vertical  distribution  of  ani- 


mals, do  the  fauna  of  a  tropical  mountain-range  resemble 
that  of  the  tropical  horizontal  zone  ?  Of  the  temperate 
zone? 

What  lines  generally  form  the  boundaries  of  animal 
regions? 

Which  possesses  the  greater  power  of  acclimation,  man 
or  the  inferior  animals? 

State  the  characteristics  of  the  tropical  fauna,  naming 


140 


PHYSICAL    GEOGRAPHY. 


the  principal  carnivora,  herbivora,  cetacea,  cheiroptera, 
marsupials,  birds,  and  reptiles. 

State  the  characteristics  of  tbe  temperate  fauna,  naming 
the  principal  carnivora,  herbivora,  rodentia,  cetacea,  mar- 
supials, birds,  and  reptiles. 

State  the  characteristics  of  the  arctic  fauna,  naming  the 
characteristic  terrestrial  and  marine  species. 

What  peculiarities  characterize  the  fauna  of  North 
America?    What  is  the  cause  of  these  peculiarities? 

What  are  the  peculiarities  of  the  fauna  of  the  South 
American  continent?  What  is  the  cause  of  these  pecu- 
liarities? 

What  is  the  main  peculiarity  of  the  Asiatic  fauna? 

Describe  the  districts  of  fur-bearing  animals  of  North 
America.     Of  Asia. 

For  what  peculiarity  are  the  animals  of  the  deserts  of 
Africa  and  Arabia  noted  ? 

What  is  the  main  characteristic  of  the  Australian  fauna  ? 


Define  ethnography. 

What  arguments  can  be  adduced  to  show  the  probable 
unity  of  the  human  race  ? 

Name  the  primary  races. 

Name  the  secondary  races. 

Into  what  three  branches  may  the  Caucasian  race  be 
divided? 

What  peoples  have  descended  from  the  Aryans,  or  the 
Indo- Europeans  ? 

Name  the  principal  Celtic  nations. 

What  nations  have  sprung  from  the  ancient  Eomans? 

What  nations  have  descended  from  the  Germans  ? 

Name  the  Slavonic  nations.    The  Iranians. 

Name  the  parts  of  the  world  inhabited  by  each  of  the 
primary  and  secondary  races. 

Describe  the  peculiarities  of  each  of  these  races. 

Name  a  few  of  the  peoples  which  belong  to  each  of  the 
races. 


MAP  QUESTIONS. 


x^Kc 


Trace  on  the  map  of  the  Vertical  Distribution  of  Ani- 
mal Life,  the  characteristic  fauna  in  those  parts  of  each 
of  the  continents,  lying  between  the  level  of  the  sea  and 
5000  feet.  Between  5000  and  10,000  feet.  Between  10,000 
and  15,000  feet.    Between  15,000  and  20,000  feet. 

Name  from  the  map  of  the  Distribution  of  Animals,  the 
tropical  species  of  the  Americas.  Of  Africa.  Of  Asia. 
Of  Australia. 

Name,  in  a  similar  manner,  the  temperate  and  arctic 
species  of  the  Americas.  Of  Europe.  Africa.  Asia.  Aus- 
tralia. 

In  what  portions  of  the  world  is  the  seal  found  ?  The 
walrus?    The  whale? 

Trace  on  the  map  the  southern  limit  of  the  polar  bear. 
Of  the  reindeer.  Of  monkeys.  Of  the  elephant  and  rhi- 
noceros.   The  northern  limit  of  the  camel.    Of  monkeys. 


Locate  the  chief  districts  of  venomous  serpents  in  the 
eastern  and  western  hemispheres. 

Describe  the  region  of  the  musk-ox.  Of  the  grizzly 
bear.    Of  the  buffalo. 

State,  from  the  Ethnographic  Map,  the  portions  of  the 
world  inhabited  by  the  Caucasian  race.  The  Mongolian 
race.  The  Ethiopian  race.  The  Malay  race.  The  Amer- 
ican race.    The  Australian  race. 

What  different  peoples  dwell  north  of  the  arctic  circle? 
South  of  the  tropic  of  Capricorn  ? 

Trace  on  the  map  the  northern  limit  of  permanent 
habitation.    The  southern  limit. 

What  race  inhabits  Hindostan  ?  What  people  ?  What 
race  inhabits  Abyssinia?  What  people?  Greenland? 
Patagonia?  China?  Mexico?  France  and  Spain ?  North- 
ern Norway  and  Sweden ?    Arabia?    Madagascar? 


Page  141 


Part  VI. 

THE  PHYSICAL  FEATURES  OF  THE  UNITED  STATES, 


►o^c 


The  civilization  and  development  of  a  country  are  dependent,  in  a  marked  degree,  on  the  pecu- 
liarities of  its  physical  features.  The  soil  and  climate  exert  their  influence  on  the  vegetable  and  animal 
life,  and  these,  in  turn,  react  on  man.  If  proper  soil  and  climate  exist ;  if  the  peculiarities  of  the 
surface  structure  permit  of  ready  intercommunication,  and  if  extensive  deposits  of  coal  and  valuable 
metals  occur,  the  future  development  of  the  country  is  assured. 

The  physical  features  of  the  magnificent  domain  of  the  United  States  are  such  as  seem  to  destine  it  to 
become  the  theatre  of  the  civilization  of  the  future.  The  peculiarities  of  its  position  and  extent,  the 
nature  of  its  soil,  the  climate,  and  rainfall,  the  size  and  constancy  of  its  navigable  rivers,  and  the  extent 
and  variety  of  its  valuable  mineral  deposits,  eminently  fit  it  to  sustain  a  very  high  order  of  civilization. 


CHAPTER  I. 

Surface  Structure  of  the  United 
States,  exclusive  of  Alaska. 

368.  Situation  and  Extent.— The  United  States 
occupies  the  entire  breadth  of  the  North  American 
continent,  between  lat.  49°  K,  and  24°  30'  K  and 
extends  from  long.  66°  50'  W.  from  Greenwich,  to 
124°  31'  W.  The  total  area,  exclusive  of  Alaska, 
is  3,026,500  square  miles. 
142 


369.  Coast  Line. — The  coast  line  is  compara- 
tively simple  and  unbroken.  On  the  east,  the 
Atlantic  Ocean  extends  into  the  land  in  three 
wide  curves ;  on  the  south,  is  the  deep  indenta- 
tion of  the  Mexican  Gulf;  on  the  west,  the  land  is 
thrust  out  into  the  Pacific  in  an  almost  unbroken 
curve.  The  total  coast  line,  exclusive  of  the  ad- 
joining islands  and  Alaska,  is  about  12,609  miles. 

370.  Gulfs  and  Bays. — The  principal  indenta- 
tions on  the  eastern  coast  are  Long  Island  Sound, 
Delaware  and  Chesapeake  Bays,  and  Albemarle 


SURFACE    STRUCTURE    OF    THE    UNITED    STATES. 


143 


and  Pamlico  Sounds.  On  the  western  coast  are 
the  Gulf  of  Georgia  and  the  fine  harbor  of  the 
Bay  of  San  Francisco. 

The  Atlantic  shores  slope  gently  toward  the 
ocean ;  the  Pacific  shores  are  abrupt. 

371.  Islands. — The  islands  of  the  Atlantic  coast 
are  of  three  distinct  classes :  those  north  of  Cape 
Cod  are,  for  the  most  part,  rocky,  and  are  de- 
tached portions  of  the  mainland ;  those  south  of 
Cape  Cod  are  generally  low  and  sandy,  and  are, 
for  the  most  part,  of  fluvio-marine  formation ;  those 
off  the  coast  of  Florida  are  of  mangrove  forma- 
tion. On  the  Pacific  coast  are  the  Santa  Barbara 
Islands,  a  rocky  group  south-west  of  California; 
and  Vancouver  Island,  north-west  of  Washington. 


Fig.  123.    View  on  the  Coast  of  Mount  Desert  Island,  Maine. 

372.  Mangrove  Islands. — Mangrove  trees  grow 
in  dense  jungles,  on  low  muddy  shores,  in  tropical 
regions.  From  both  trunks  and  branches  the 
trees  throw  out  air-roots,  which  spread  so  as  to 
cover  the  adjoining  spaces  in  an  almost  intermin- 
able network  of  roots  and  branches.  The  area  of 
surface  covered  by  the  trees  is  still  further  in- 
creased by  the  curious  property  which  the  seeds 
possess  of  sprouting  while  on  the  tree,  subse- 
quently floating  away,  and  afterward  affixing 
themselves  to  the  bottom  of  the  jungle,  to  form 
new  growths.  In  this  way,  the  trees  form  man- 
grove islands,  which  at  first  are  not  true  islands, 
the  trees  simply  standing  above  the  water  by 
means  of  their  intertwined  roots.  In  course  of 
time,  however,  sediment,  collecting  between  the 
roots  of  the  trees,  forms  islands.  These  islands 
are  common  in  the  shallow  water  off  the  coasts 
of  Florida. 

373.  Coral  Reefs  of  Florida. — The  peninsula 
of  Florida,  south  of  the  northern  extremity  of  the 
Everglades,  and  probably  as  far   north   on  the 


eastern  coast  as  St.  Augustine,  is,  according  to 
Agassiz,  a  species  of  coral  formation,  formed, 
however,  under  different  conditions  than  are  the 
coral  islands  of  the  Pacific. 


Fig.  124.    Florida  Reefs  and  Keys,  (LeOonte.) 


Fig.  125.    Everglades,  Reefs,  and  Keys  of  Florida,  (LeOonte.) 

Figure  124  is  a  map  of  Florida  with  its  reefs  and  keys. 
Figure  125,  is  a  section  along  the  line  A.  A.  In  Fig.  124 
the  line  a  a,  shows  what  was  at  one  time  the  limit  of  the 
southern  coast  of  Florida.  6  b,  is  the  present  limit  of  the 
southern  coast,  cc,  are  the  keys,  which  are  low  islands. 
dd,  is  the  growing  coral  reef,  e,  is  the  Everglades,  dotted 
with  islands,  called  hummocks.  Between  c  c,  and  d  d,  is 
the  ship  channel.  Outside  the  growing  coral  reef  dd,  are 
the  profound  depths  of  the  Gulf  Stream  G.  S. 

The  growth  of  the  reef-formations  is  explained  hy 
LeConte  as  follows  (Fig.  125) :  a,  was  at  one  time  the  limit 
of  the  southern  coast  of  Florida.  6,  is  the  present  southern 
coast,  which  at  one  time  was  a  coral  reef  like  d.  Upon  b, 
a  line  of  coral  islands  gradually  formed  connecting  it 
with  the  old  southern  coast  a.  The  ship  channel  between 
a,  and  b,  gradually  filled  up  and  formed  the  Everglades  e. 
Meanwhile,  another  reef  formed,  in  the  position  of  the 
present  keys,  c,  the  ship  channel  being  between  6,  and  c. 
This  reef  has  now  grown  to  be  a  line  of  coral  islands, 
and  the  ship  channel,  between  6,  and  c,  converted  into 
shoals  and  mud  flats,  /.  The  present  ship  channel  is 
between  c,  and  d.  In  course  of  time  the  southern  coast 
will  extend  to  the  present  line  of  keys,  c,  and  the  shoal 
water  /,  will  become  another  Everglades.  Outside  the 
present  keys  c,  another  coral  reef  d,  is  growing,  to  which 
the  coast  will  ultimately  extend,  and  which  will  mark 
the  limit  of  the  formation,   owing  to  the  deep  waters 


144 


PHYSICAL    GEOGRAPHY. 


of  the  Gulf  Stream,  immediately  beyond  it.  In  Figure 
125,  the  dotted  lines  show  the  successive  steps  of  the 
formation. 

374.  Forms  of  Relief. — The  United  States  is 
traversed  by  two  distinct  mountain-systems :  the 
Pacific  System — the  predominant  system— on  the 
west,  and  the  Appalachian  System — the  secondary 
system — on  the  east. 

375.  The  Pacific  System,  consists  of  a  broad 
plateau,  traversed  by  two  distinct  mountain-sys- 
tems: the  Rocky  Mountains,  and  the  Pacific 
mountain-chains.  It  embraces  about  one-third 
of  the  entire  territory  of  the  United  States 
proper. 

376.  The  Rocky  Mountain  System,  consists  of 
a  number  of  parallel  chains  connected  by  numer- 
ous cross  ranges.  They  rise  from  the  summits  of 
an  elevated  plateau,  which  in  some  places  is  fully 
7000  feet  above  the  sea.  The  chains  are  broken 
in  several  places  by  transverse  valleys  or  passes, 
traversed  by  important  rivers.  The  most  import- 
ant of  these  passes  is  South  Pass,  in  Wyoming, 
traversed  by  the  Sweet  Water  River,  a  tributary 
of  the  Platte.  The  Missouri,  Rio  Grande,  and 
other  rivers  also  flow  through  similar  depressions. 

The  chains  are  separated  into  northern  and  southern 
sections  by  a  gap  occupied  by  an  elevated  plateau,  over 
which  the  Union  Pacific  Railroad  passes. 

Among  the  many  lofty  peaks  of  this  mountain- 
system  are  Long's  Peak,  14,050  feet ;  Pike's  Peak, 
14,216  feet ;  and  Fremont's  Peak,  13,570  feet  high. 

A  remarkable  feature  of  these  mountains  is  the  basin- 
shaped  valleys,  called  parks,  formed  by  transverse  ranges 
connecting  the  parallel  ranges.  The  most  important  of 
these  parks  are  North,  South,  and  Middle  Parks.  They 
are  nearly  rectangular  in  outline,  and  are  hemmed  in  by 
huge  mountain-ranges.  Each  parfi;  gives  rise  to  an  im- 
portant river.  The  rich  verdure  of  these  deeply-sunken 
basins  is  rendered  the  more  striking  by  contrast  with  the 
desolate  mountains  surrounding  them. 

The  Yellowstone  National  Park,  in  the  north-western 
part  of  Wyoming,  is  traversed  by  some  of  the  head-waters 
of  the  Yellowstone  Eiver.  It  is  a  region  of  hot  springs, 
deep  gorges,  high  mountain-peaks,  and  magnificent  scenery. 
It  has  been  set  apart  by  the  government  for  the  purposes  of 
a  public  park. 

The  Great  Plains,  an  elevated  plateau,  lie 
along  the  eastern  side  of  the  Rocky  Mountains. 
They  are  undulating  plains,  which  slope  by 
almost  imperceptible  gradations,  to  the  valley 
of  the  Mississippi.  They  are  treeless,  and  near 
the  base  of  the  mountains  have  but  a  scanty 
vegetation.  Near  the  lower  part  of  the  slope 
they  merge  into  prairies,  covered  with  a  luxuri- 
ant growth  of  grass. 


377.  The  Pacific  Mountain-Chains  extend 
through  California,  Oregon,  and  Washington, 
and,  in  general,  are  parallel  to  the  Rocky  Moun- 
tains. They  comprise  the  Cascade  Mountains  in 
Oregon  and  Washington,  and  the  Sierra  Nevada 
and  the  Coast  Mountains  in  California. 

The  famous  gold  regions  of  California  lie  mainly  west 
of  the  Sierra  Nevada  and  the  Coast  Mountains. 

The  loftiest  peaks  of  the  Pacific  Mountain- 
chain  exceed  those  of  the  Rocky  Mountains  in 
height.  The  highest  peaks  are  Mt.  Rainier  in 
the  Cascade  Range,  14,444  feet  high ;  and  in  the 
Sierra  Nevada  Range,  Mt.  Shasta,  14,482  feet 
high,  and  Mt.  Whitney,  14,800  feet  high. 

The  culminating  point  of  the  Pacific  Mountain- 
chains  is  Mount  St.  Elias,  in  Alaska,  which  is  es- 
timated to  be  19,500  feet  high. 

The  Cascade  Mountains  contain  numerous  ex- 
tinct volcanoes. 

The  Great  Basin  lies  between  the  Wahsatch  on  the  east, 
and  the  Sierra  Nevada  and  Cascade  ranges  on  the  west, 


Fig.  126.    The  Great  OaSon  of  Colorado. 

It  possesses  a  true  inland  drainage.    East  of  the  Wahsatch 
Mountains  and  the  western  flanks  of  the  elevated  peaks 


SURFACE    STRUCTURE    OF    THE    UNITED    STATES. 


145 


and  ranges  of  Colorado,  lies  a  region  drained  by  the  head- 
waters of  the  Colorado.  This  region,  together  with  the 
country  lying  in  the  middle  courses  of  the  river,  is  a  won- 
derful section  of  country,  traversed  by  streams  that  have 
eroded  their  valleys  and  flow  through  deep  canons,  some 
of  which  are  over  6000  feet  deep.  A  view  of  a  part  of  one 
of  the  most  noted  of  these  canons  is  shown  in  Fig.  126. 

378.  The  Appalachian  System,  sometimes  called 
the  Alleghany  Mountains,  extends  from  Georgia 
to  Maine,  nearly  parallel  to  the  Atlantic.  The 
chain  varies  in  breadth  from  150  to  200  miles. 
The  system  consists  of  an  elevated  plateau, 
bearing  several  mountain-chains,  separated  by 
wide  valleys.  In  the  northern  and  southern 
parts  of  the  chain,  where  the  elevation  is  the 
greatest,  the  system  is  formed  of  irregular  groups, 
without  any  definite  direction.  In  the  centre, 
low  parallel  chains  occur  separated  by,  fertile  val- 
leys. These  valleys  generally  take  the  names  of 
the  rivers  which  flow  through  them. 

The  system  is  highest  in  North  Carolina,  where 
Mt.  Mitchell,  6707  feet  high,  forms  its  culminat- 
ing point. 

Beginning  in  the  north,  the  system  includes  the 
White  Mountains  in  New  Hampshire,  with  Mount 


Fig.  127.    The  Natural  Bridge  (Virginia). 

Washington,  6294  feet  high  ;  the  Green  Mountains, 
in  Vermont ;  the  Adirondacks,  in  New  York,  with 


the  culminating  peak  of  Mount  Marcy,  5379  feet 
high ;  the  Catskill  Mountains,  the  Blue  Mountains, 
the  Alleghanies,  the  Blue  Ridge,  the  Cumberland 
Mountains,  and  others. 

The  Natural  Bridge,  in  Bockbridge  County,  Virginia, 
is,  from  its  peculiar  formation,  an  object  of  interest  to 
tourists. 

379.  Plains. — There  are  two  great  low  plains 
in  the  United  States:  the  Atlantic  Coast  Plain 
and  the  Plain  of  the  Mississippi  Valley. 

The  Atlantic  Coast  Plain  lies  along  the  eastern 
flanks  of  the  Appalachian  Mountains.  It  varies 
in  width  from  50  to  250  miles.  Along  the  coast 
the  soil  is  comparatively  sandy,  and  has  been 
formed  by  the  combined  action  of  the  rivers  and 
ocean. 

The  extensive  swamps  which  occur  in  this  region — such 
as  Cypress  Swamp,  in  Delaware,  Dismal  Swamp,  north  of 
Albemarle  Sound,  Alligator  Swamp,  between  Albemarle 
and  Pamlico  Sounds,  and  Okefinokee  Swamp,  in  Southern 
Georgia — are  of  fluvio-marine  origin.  The  Everglades,  in 
Florida,  are  the  result  of  a  coral  formation.  Farther  from 
the  coast,  the  plain  is  more  elevated ;  long  valleys  occur, 
which  are  very  fertile,  particularly  near  the  river  bottoms. 

The  Mississippi  Valley  lies  between  the  predomi- 
nant and  the  secondary  mountain-systems.  It  is 
over  300,000  square  miles  in  area,  and  includes 
some  of  the  most  fertile  land  in  the  country. 
Much  of  it  is  covered  with  forests  or  prairies. 

380.  River-  and  Lake-Systems. — The  United 
States  is  particularly  noted  for  the  number  and 
extent  of  its  navigable  rivers. 

Oceanic  Drainage — Atlantic  System. —Among 
the  important  rivers  emptying  directly  into  the 
Atlantic  Ocean  are  the  Penobscot,  Merrimac, 
Connecticut,    Hudson,   Delaware,    Susquehanna, 


Fig,  128.    Scene  on  the  Mississippi. 

Roanoke,  Cape  Fear,  Santee,  Savannah,  Alta- 
maha,  and  the  St.  John's. 


146 


PHYSICAL    GEOGRAPHY. 


Of  the  rivers  flowing  into  the  Mexican  Gulf, 
the  Appalachicola,  Alabama,  Mississippi,  Sabine, 
Trinity,  Brazos,  Colorado,  and  the  Rio  Grande  are 
the  most  important. 

The  Mississippi,  faking  its  origin  in  the  head-waters  of 
the  Missouri — which  is  the  true  parent  stream — is  the  long- 
est river  in  the  world,  its  length  being  4490  miles.  Its 
tributaries  are,  in  general,  navigable  for  great  distances, 
and  thus  afford  ready  communication  with  different  parts 
of  the  basin.  The  important  tributaries  of  the  Mississippi 
on  the  west  are  the  Minnesota,  the  Missouri,  the  Arkansas, 
and  the  Eed.  On  the  east,  the  Wisconsin,  the  Illinois,  and 
the  Ohio. 

The  Pacific  System. — The  principal  rivers  emp- 
tying into  the  Pacific  Ocean  are  the  Columbia, 
Sacramento,  San  Joaquin,  and  the  Colorado. 

381.  Inland  Drainage. — The  rivers  and  lakes 
of  the  Great  Basin  have  no  outlet  to  the  ocean, 
and  therefore  form  true  steppe  systems.  Great 
Salt  and  Humboldt  lakes  are  the  principal  lakes, 
and  the  Humboldt  and  the  Reese,  the  principal 
rivers. 

There  are  two  regions  in  the  United  States  below  the 
mean  level  of  the  sea: 

(1.)  In  the  southern  part  of  California,  in  Soda  Valley, 
200  feet  below  the  sea. 

(2.)  Death  Valley  in  Eastern  California.  These  regions 
are  extremely  arid.' 

382.  Lake-Systems. — The  most  important  lake- 
system  of  the  United  States  lies  in  the  northern 
part.  It  includes,  among  numerous  others,  five 
of  the  largest  fresh-water  lakes  in  the  world: 
Superior,  Michigan,  Huron,  Erie,  and  Ontario. 
From  their  immense  extent,  they  resemble  great 
inland  seas. 

Numerous  fluviatile  or  river  lakes  occur  near  the  borders 
of  the  middle  and  lower  courses  of  the  Mississippi  and  its 
tributaries.  They  are  nearly  all  found  in  the  States  west 
of  the  Mississippi. 


-~oJ«<c 


CHAPTER   II. 
Meteorology. 

383.  Climate.— The  United  States,  exclusive  of 
Alaska,  lies  entirely  within  the  limits  of  the  mathe- 
matical north  temperate  zone. 

Physical  Zones. — As  regards  the  actual  distri- 
bution of  heat,  the  United  States  lies  between 
the  annual  isothermal  lines  of  40°  and  77°  Fahr. 
Its  territory  therefore  embraces  two  zones  of  phys- 
ical climate,  the  physical  north  temperate  and  the 
physical  torrid  zones.  The  isotherm  of  70°,  the 
boundary   of   the   physical    torrid    zone,   passes 


through  Florida,  Louisiana,  Texas,  and  Arizona. 
All  of  the  country  south  of  this  line  lies  in  the 
physical  torrid  zone ;  all  north  of  it,  in  the 
physical  north  temperate  zone. 

The  Territory  of  Alaska  lies  in  the  north  frigid 
and  north  temperate  zones. 

384.  Mean  Annual  Isotherms. — The  following  pecu- 
liarities in  the  mean  annual  distribution  of  heat,  will  be 
seen  from  a  study  of  the  mean  annual  isotherms  on  the 
map  (page  141) : 

The  isotherm  of  40°,  the  lowest  mean  annual  tempera- 
ture, is  found  in  a  few  elevated  districts  in  New  England, 
in  the  elevated  districts  around  Lake  Superior,  and  in  the 
higher  plateaus  of  the  Eocky  Mountains. 

The  isotherm  of  45°,  east  of  the  Mississippi,  runs  slightly 
north  of  the  44°  of  N.  lat.,  and,  except  in  New  York,  Ver- 
mont, and  New  Hampshire,  is  nearly  parallel  with  it.  In 
the  Dakotas  it  bends  toward  the  north-west,  reaching 
the  northern  boundary  of  the  United  States  in  Mon- 
tana, when  it  bends  suddenly  toward  the  south-east,  until 
it  reaches  Central  Colorado,  where,  nearly  parallel  with 
its  southward  deflection,  it  again  turns  abruptly  to  the 
north. 

The  isotherm  of  50°  is  nearly  parallel  with  the  41°  N. 
lat.,  until  it  reaches  Colorado,  when  it  bends  sharply  south 
to  the  36°  lat. ;  then  it  extends  in  a  nearly  direct  line 
toward  the  north-west,  entering  the  Pacific  coast  some- 
what to  the  north  of  Washington. 

The  isotherm  of  55°  enters  the  Atlantic  coast  at  lat.  40° ; 
it  then  extends  south-west  to  Tennessee;  thence  north- 
ward to  Kentucky,  from  which  its  course  is  nearly  due 
west  to  Indian  Territory,  when  it  bends  southward  to 
about  lat.  34°  in  New  Mexico.  From  this  point  it  extends 
in  a  nearly  direct  north-westerly  course  to  lat.  41°  in 
Northern  California,  when  it  bends  sharply  to  the  south, 
entering  the  Pacific  Ocean  at  about  lat.  36°. 

The  isotherm  of  52.5°,  traced  only  on  the  western  half 
of  the  map,  starts  from  the  north-western  part  of  New 
Mexico,  and  runs  in  a  nearly  direct  north-westerly  course 
to  North-eastern  Nevada,  when  it  divides,  the  northern 
branch  extending  to  the  north-western  extremity  of 
Washington,  and  the  southern  entering  the  Pacific  in 
the  neighborhood  of  San  Francisco. 

The  isotherm  of  60°  enters  the  Atlantic  coast  at  Norfolk, 
Virginia ;  it  then  trends  south-west  to  Northern  Georgia, 
from  which  its  course  is  nearly  due  west  until  it  reaches 
Indian  Territory,  when  it  runs  south-west  to  New  Mexico. 
Here  it  divides  into  two  branches :  the  northern  extends 
in  irregular  curves  to  lat.  40°  in  California,  when  it  bends 
sharply  to  the  south-east,  entering  the  Pacific  at  about  lat. 
34°.  The  southern  branch  enters  the  Gulf  of  California 
at  about  lat.  25°. 

The  isotherm  of  70°  extends  through  Northern  Florida, 
Southern  Louisiana,  and  Texas. 

The  isotherm  of  75°  extends  through  Southern  Florida. 

385.  Climatic  Contrasts. —  There  is  a  marked 
contrast  between  the  climate  of  the  eastern  and 
western  coasts  of  the  United  States.  The  eastern 
coast  is  colder  than  the  western. 

The  difference  in  temperature  is  greater  in  the 
north  ;  the  mean  annual  temperature  of  the  coast, 
between  New  Jersey  and  Maine,  is  from  52°  to 


METEOROLOGY. 


147 


42°  Fahr.,  while  on  the  shores  of  California, 
Oregon,  and  AVashington,  the  mean  is  nowhere 
lower  than  52°,  and  in  many  places  is  much 
higher. 

In  the  southern  portions  of  the  eastern  and 
western  coasts,  the  contrast  is  not  so  decided, 
owing  to  the  peculiarly  cool  summers  in  the  west- 
ern part  of  the  continent. 

The  Atlantic  seaboard  is  much  colder  than  corresponding 
latitudes  on  the  western  coasts  of  Europe.  For  example, 
the  latitude  of  New  York  City  is  about  the  same  as  that 
of  Madrid,  Naples,  and  Constantinople;  of  Boston,  the 
same  as  that  of  Rome;  of  Portland,  Maine,  the  same  as 
that  of  Marseilles;  of  Quebec,  nearly  that  of  Paris;  and 
yet  what  a  striking  difference  in  their  climates ! 

The  western  shores  of  America  are,  however,  quite  as 
warm  as  those  of  Europe.  Sitka,  in  lat.  57°,  has  a  winter 
mean  very  nearly  the  same  as  that  of  Edinburgh,  in  the 
same  latitude. 

The  higher  mean  annual  temperature  of  the  western 
coasts  over  that  of  the  eastern  will  prove  of  great  signifi- 
cance in  the  future  history  of  the  United  States,  since  our 
western  shores  will  admit  of  cultivation  and  settlement  for 
a  much  greater  distance  north  than  will  the  eastern.  "  The 
difference,"  says  Blodget,  "covers  12°  to  15°  of  latitude  on 
the  coast  of  the  Pacific,  and  from  5°  to  40°  on  the  plains 
east  of  the  Rocky  Mountains. 

The  sharp  contrast  between  the  climate  of  the 
eastern  and  western  shores  is  caused  by  the  at- 
mospheric and  oceanic  circulation,  which,  in  both 
cases,  is  from  west  to  east;  hence,  the  higher  tem- 
perature of  the  western  shores,  on  account  of  the 
warm,  vapor-laden  winds  from  the  Pacific,  the 
comparatively. heavy  rainfall,  and  the  warm  ocean 
currents.  The  cold  Arctic  current,  which  comes 
from  Baffin  Bay  down  the  Atlantic  seaboard, 
reduces  the  mean  annual  temperature  of  the 
eastern  coast. 

On  the  south,  the  Gulf  Stream,  emerging  from 
between  Florida  and  Cuba,  tends  to  raise  the  tem- 
perature of  the  southern  portions  of  the  seaboard, 
though  its  greatest  influence  is  exerted  on  the  dis- 
tant shores  of  Europe.  On  the  Pacific  coast,  the 
Japan  current,  after  leaving  the  Asiatic  shores, 
flows  southward  along  the  North  American  coasts, 
bathing  them  with  its  highly  heated  waters. 

386.  Constancy  of  the  Climate.— From  obser- 
vations extending  back  as  far  as  the  year  1738,  it 
appears,  that  from  that  time,  the  climate  of  the 
United  States  has  undergone  no  decided  change. 

387.  Distribution  of  Wind  and  Rain.— The 
United  States  lie  in  the  zone  of  the  variable 
winds.      Westerly  winds,  therefore,  predominate. 

388.  Precipitations.  —  The  domain  of  the 
United  States  is  well  watered,  copious  rains  fall- 
ing over  nearly  all  portions  of  the  surface,  espe- 


cially on  those  which  lie  east  of  the  predominant 
mountain-system. 

East  of  the  100th  meridian  from  Greenwich, 
an  average  of  at  least  40  inches,  or  3i  feet,  falls 
throughout  the  year.  From  this  large  rainfall, 
it  is  evident  that  the  evaporation,  which  supplies 
the  winds  with  moisture,  must  take  place  in  the 
equatorial  regions,  and  that,  in  general,  the  upper 
currents  of  equatorial  winds  bring  the  rain.  The 
open  sweep  afforded  to  the  winds  by  the  Gulf  of 
Mexico  and  the  Mississippi  Aralley,  increases  the 
rainfall  of  the  Gulf  States. 

The  heaviest  annual  rainfall  is  65  inches,  and' 
occurs  near  the  borders  of  the  Gulf  States,  and 
along  the  Pacific  seaboard  in  AVashington  and 
Oregon.  Along  the  Atlantic  border,  it  varies 
from  40  to  45  inches ;  in  the  upper  half  of  the 
Mississippi  Valley,  it  varies  from  25  to  40  inches ; 
in  the  lower  half,  from  40  to  65  inches ;  in  the 
upper  course  of  the  Missouri  and  the  region  of 
the  Yellowstone,  from  20  to  22  inches;  in  por- 
tions of  the  Great  Basin  the  rainfall  is  very 
limited,  being  but  from  5  to  10  inches. 

As  regards  its  distribution  in  time,  rain  is  pos- 
sible at  all  seasons  of  the  year  over  most  of  the 
country ;  over  some  portions,  however,  it  is  peri- 
odical in  character,  these  districts  having  a  rainy 
and  a  dry  season. 

East  of  the  Mississippi  River,  rain  may  fall  at 
any  time  of  the  year.  Near  the  Atlantic  coast, 
rain  is  especially  abundant  in  the  spring. 

AVest  of  the  Mississippi  the  rainfall  is  more 
irregular.  In  AVashington,  on  the  Pacific  coast, 
rain  may  fall  at  any  time  during  the  year. 
On  other  parts  of  the  Pacific  coast,  rain  is  most 
frequent  in  winter;  during  the  summer,  it  is 
either  scanty  or  wholly  absent.  This  periodicity 
in  the  distribution  occurs  mainly  in  the  region 
near  the  coast.  In  the  interior,  the  precipitation 
is  more  irregular. 

389.  The  Weather  Bureau. — Considerable  light 
has  been  thrown  on  the  meteorological  conditions 
of  the  United  States  by  the  operations  of  the 
"Weather  Bureau." 

The  AVeather  Bureau  was  established  by  an 
Act  of  Congress  in  February,  1870,  authorizing 
the  Secretary  of  War  to  establish  and  equip 
stations  in  different  parts  of  the  country,  where 
such  simultaneous  observations  of  the  meteor- 
ological conditions  of  the  atmosphere  could  be 
taken,  as  would  enable  the  Department  to  give 
timely  notice  to  all  important  ports  on  the  Atlantic 


B  Mt.       WEATHER  MAP,  SHOWING  CONDITION  OF  THE  WEATHER  ON  A  CERTAIN  BAY  IN  APRIL . 


WEATHER  SIGNALS. 


Rain  or  Snow 
followed  by 
Cold  Wave 


STORM   SIGNALS  . 


Cautionary 


Westerly  Win  ds 


METEOROLOGY. 


149 


eoast  and  Great  Lakes  of  the  approach  of  danger- 
ous storms,  and  to  collect  such  information  as 
would  be  of  value  to  shipping  and  other  interests. 

In  1890,  the  direction  of  the  Weather  Bureau  was,  by 
Act  of  Congress,  taken  from  the  War  Department  and 
transferred  to  the  Department  of  Agriculture. 

There  are  about  500  stations  established  by 
the  Weather  Bureau  in  different  sections  of 
the  United  States.  At  these  stations  there  are 
trained  and  intelligent  observers,  who  several 
times  each  day  are  simultaneously  required  to 
make  careful  observations  of  the  temperature, 
humidity,  and  pressure  of  the  air,  the  direction 
and  force  of  the  wind,  the  clearness  or  cloudiness 
of  the  sky,  and  the  amount  of  rain  or  snow  that 
has  fallen  during  a  given  time. 

These  observations  are  telegraphed  to  the  Cen- 
tral Office  at  Washington,  so  that  the  Bureau  is 
enabled  to  see  the  actual  meteorological  condi- 
tions which  exist  throughout  the  country  at  any 
given  time,  and  from  such  knowledge,  guided  by 
previous  experience,  to  prepare  "synopses"  of 
the  weather  and  "  indications,"  or  forecasts. 

For  the  preparation  of  the  "indications"  the  officer  in 
charge  prepares  a  number  of  graphic  charts,  based  on  the 
various  data  telegraphed  to  the  Central  Office,  as  the  result 
of  the  simultaneous  observations  at  the  different  stations. 
These  charts  exhibit  the  actual  meteorological  conditions 
that  then  exist,  those  that  existed  during  the  previous 
eight  hours,  and  the  previous  twenty-four  hours,  and  the 
conditions  normal  for  the  place  at  that  particular  time  of 
the  year.  The  data  shown  on  these  charts  include  the 
temperature,  barometric  pressure,  humidity  of  the  air, 
precipitation,  condition  of  sky,  force  and  direction  of 
wind,  etc.  The  "  indications  "  are  telegraphed  to  the  press 
throughout  the  country.  In  general  about  85  per  cent,  of 
these  indications  are  verified. 

It  should  be  borne  in  mind,  in  considering  this  very 
large  percentage  of  verified  forecasts,  that  the  indications 
are  predicted  for  extended  areas,  and,  therefore,  although 
the  change  may  not  have  occurred  in  some  limited  section 
of  the  predicted  area,  it  may  have  occurred  in  nearly  all 
r  the  other  portions  of  the  region. 

Changes  in  the  Weather — Passage  of  a  Great 
Storm. — Since  nearly  all  the  great  storms  of  the 
United  States  are  species  of  cyclones,  that  move 
aver  the  country  in  a  general  easterly  direction, 
when  such  a  storm  is  once  started  it  is  not  a  dif- 
ficult matter  to  predict  its  general  path,  and  thus 
foretell  coming  changes  in  the  weather. 

The  principal  elements  of  uncertainty  are  the  exact  path 
in  which  the  storm  will  move  over  the  country,  and  the 
velocity  of  such  motion.  These  the  bureau  can  predict, 
approximately,  from  a  comparison  of  all  the  previous 
storms  of  which  it  has  records. 

The  whirling  direction  of  the  wind  in  the  Northern 
Hemisphere  is  in  the  opposite  direction  to  that  of  the 
17 


hands  of  a  watch.  Therefore,  as  the  eastern  side  of  a 
storm  approaches  any  section  of  country,  the  winds  blow 
generally  from  the  south  toward  the  north.  The  approach 
of  a  cyclone  is  generally  attended  by  a  fall  of  rain  or  snow. 
As  the  cyclone  moves  onward,  and  its  western  side  passes 
over  any  locality,  the  general  direction  of  the  wind  is 
from  the  north  to  the  south.  The  passing  of  the  cyclone 
is  generally  attended  by  clearing,  cooler  weather. 

Cold  Waves. — On  the  edges  of  a  cyclone  the 
barometer  is  high.  When  one  storm  follows  an- 
other at  a  short  interval,  the  area  of  high  ba- 
rometer between  them  causes  the  wind  to  blow  in 
all  directions  from  the  centre  of  high  barometer, 
and  a  cyclonic  movement  of  the  air  is  thus  es- 
tablished, possessing  a  progressive  motion  like  a 
true  cyclone.  Since  the  direction  of  rotation  of 
such  a  storm  is  opposite  to  that  of  a  cyclone,  it 
is  called  an  anti-cyclone.  Cold  waves  generally 
originate  in  anti-cyclones. 

The  Weather  Signals  consist  of  signal-flags 
displayed  at  important  stations  on  the  various 
lines  of  railroads  and  at  other  prominent  places, 
and  are  designed  to  indicate  the  probable  weather 
and  temperature  of  the  coming  day. 

The  temperature  signal  indicates  warmer  weather  when 
placed  above  the  other  flags,  and  colder  weather  when 
placed  below  them.  The  cold-wave  flag  indicates  a  de- 
cided fall  in  temperature. 

The  Storm  Signals  are  displayed  at  all  ports  on 
the  Great  Lakes  or  the  Atlantic  seaboard  whenever 
it  is  considered  probable  that  within  twelve  hours 
there  will  be  experienced  at  those  ports,  or  within 
one  hundred  miles  thereof,  a  wind  dangerous  to 
navigation.  The  cautionary  signal  is  displayed 
when  the  winds  expected  will  be  severe,  but  not 
dangerous  to  well-equipped  vessels. 

In  order  to  extend  the  benefits  of  the  "  indica- 
tions "  to  the  agricultural  districts,  farmers'  bul- 
letins, containing  forecasts,  are  issued  daily. 

To  reach  the  different  cities,  towns,  and  villages,  and  the 
hamlets  of  the  rural  districts,  the  indications,  or  forecasts, 
are  telegraphed  every  midnight  from  the  Central  Office  to 
centres  of  distribution,  situated  in  different  States.  These 
reports  are  at  once  printed  at  each  of  these  distributing 
stations,  enclosed  in  envelopes,  and  forwarded  to  every 
post-office  which  can  be  reached  by  the  swiftest  mail 
facilities  by  2  p.  M.  of  the  next  day.  Great  benefit  is 
thus  conferred  on  agricultural  interests. 

Warnings  of  coming  floods,  movements  of  river  ice, 
sudden  or  unusual  change  of  level  in  rivers,  are  also  given 
as  the  occasion  warrants.  The  warning  is  given  whenever 
the  water  rises  above  a  certain  level,  called  the  danger  level. 

Another  series  of  reports  are  for  the  benefit  of  internal 
navigation.  They  consist  in  the  announcement,  from  day 
to  day,  of  such  changes  of  temperature  for  different  sec- 
tions of  the  country  as  would  be  likely  either  to  stop 
navigation  by  the  freezing  of  the  canals,  or  temporarily 


150 


PHYSICAL    GEOGRAPHY. 


to  open  them  sufficiently  to  enable  ice-bound  vessels  to  be 
pressed  forward  to  the  termini  of  the  canals. 

The  value  of  the  Weather  Bureau  can  scarcely  be  over- 
estimated ;  the  saving  of  shipping  effected  by  the  timely 
warning  of  a  single  severe  storm  may  more  than  pay  the 
entire  expenses  of  the  bureau  for  a  large  portion  of  the 
year.  We  append  the  following  resume  of  the  work  of 
the  bureau : 

(1.)  The  announcement  of  probable  weather  changes  by 
the  publication  of  "  indications." 

(2.)  The  timely  warning  of  the  approach  of  severe 
storms. 

(3).  The  display  of  signals  indicating  coming  changes  in 
the  weather. 

(4).  The  publication  of  farmers'  bulletins. 

(5.)  The  river  and  canal  reports. 

(6.)  The  display  of  symbol-maps,  showing  the  actual 
state  of  the  weather  throughout  the  entire  country. 

(7.)  The  publication  of  daily  weather  maps,  monthly 
charts,  and  charts  which  give  the  results  of  the  observa- 
tions of  years. 

(8.)  The  publication  of  cotton -region  reports,  embracing 
reports  of  rainfall  and  maximum  and  minimum  tempera- 
ture throughout  the  cotton  districts  from  April  1  to 
October  31. 

The  International  Weather  Service. — The  suc- 
cess of  the  meteorological  observations  of  the  U.  S. 
Weather  Bureau  has  led  to  the  establishment  of 
stations  for  simultaneous  observations  over  a  large 
portion  of  the  northern  hemisphere  and  some  sta- 
tions in  the  southern  hemisphere.  By  simulta- 
neous observations  of  the  meteorological  conditions 
of  the  whole  earth,  many  things  yet  unknown  as  to 
weather  predictions  are  likely  to  be  discovered. 

Tornadoes  resemble  cyclones  in  that  they  are 
whirling    motions   of   the   air.     The   area   over 


Pig.  129.    A  Tornado. 

which  they  extend  is  more  limited,  but  the 
velocity  of  the  wind  is  higher  than  in  cyclones, 
and,  therefore,  their  destructive   power   is  very 


great.  When  they  pass  over  any  section  of 
country  they  leave  devastation  and  ruin  in  their 
track. 

Tornadoes  are  of  frequent  occurrence  in  the 
central  and  western  portions  of  the  Mississippi 
Valley. 

Tornadoes  have  their  origin  in  a  rotary  motion 
imparted  to  a  mass  of  warm  moist  air  that  is 
temporarily  imprisoned  below  a  mass  of  colder 
air.  The  whirling  motions  begin  at  the  upper  ex- 
tremity of  the  column,  near  the  cold  air,  and 
gradually  extend  downwards.  This  produces  the 
characteristic  inverted  funnel-shaped  mass  of 
dark  cloud  by  which  the  approach  of  a  tornado 
is  generally  heralded. 

The  path  of  the  tornado,  like  that  of  the 
cyclone,  is  generally  eastward. 

Weather  Maps. — The  actual  condition  of  the  weather 
over  the  United  States,  on  any  day,  is  represented  in 
weather  maps  published  by  the  bureau.  Two  such  maps 
are  shown  on  page  148.  The  upper  map  shows  the  meteor- 
ological conditions  prevailing  on  a  certain  day  in  April. 
On  that  day  an  area  of  low  barometer  existed  in  Colorado, 
Nebraska,  and  Kansas,  within  which  the  barometer  was 
below  29.5  inches,  as  shown  by  the  isobar,  or  line  of  mean 
barometric  pressure,  of  29.5.  The  country  around  this 
area  had  a  gradually  increasing  barometric  pressure,  as 
indicated  by  the  successive  isobars  29.6,  29.7,  29.8,  29.9, 
etc.  At  the  same  time  a  storm  was  moving  toward  the 
north-east,  as  shown  by  the  line  of  crosses.  The  rate  of 
progress  of  the  storm  being  known,  the  bureau  issued  the 
following 

Indications. 

For  New  England,  fair  weather  followed  by  light  rains 
to-morrow,  north  to  east  winds,  slight  rise  in  temperature. 

For  the  Middle  Atlantic  States,  increasing  cloudiness  and 
rain,  winds  shifting  to  east  and  south,  slightly  warmer 
weather,  lower  barometer. 

For  the  South  Atlantic  States,  local  rains,  warmer,  partly 
cloudy  weather,  south-east  to  south-west  winds,  lower  ba- 
rometer. 

For  the  East  Gulf  States,  threatening  weather  and  rain, 
followed  by  clearing  weather,  southerly  to  westerly  winds, 
slight  rise  in  temperature,  followed  in  west  portion  by  a 
slight  fall  in  temperature. 

For  the  West  Gulf  States,  local  rains,  followed  by  clear- 
ing weather,  winds  shifting  to  west  and  north,  nearly  sta- 
tionary, followed  by  lower  temperature,  and  rising  barom- 
eter to-morrow. 

For  Tennessee  and  the  Ohio  Valley,  cloudy  weather  and 
rain,  southerly  to  westerly  winds,  rising  temperature,  fall- 
ing barometer  and  severe  local  storms,  followed  to-mor- 
row in  west  portion  by  cooler  weather  and  higher  barom- 
eter. 

For  the  Lower  Lake  Region,  threatening  weather  and 
rain,  east  to  south  winds,  lower  barometer  and  rising 
temperature. 

For  the  Upper  Lake  Region,  threatening  weather,  with 
rain  or  snow,  north-easterly  winds  becoming  variable,  fall- 
ing followed  by  rising  barometer,  slight  rise,  followed  by 
falling  temperature. 


VEGETABLE    AND    ANIMAL    LIFE. 


151 


For  the  Upper  Mississippi  Valley,  threatening  weather 
and  rain,  severe  local  storms,  winds  shifting  to  west  and 
north,  followed  by  higher  barometer  and  colder  weather. 

For  the  Missouri  Valley,  rain  or  snow,  generally  colder, 
cloudy  followed  by  partly  cloudy  weather,  dangerous  local 
storms  in  southern  portion,  winds  shifting  to  north  and 
west,  with  colder  weather  and  higher  barometer. 

Light  rains  are  indicated  to-morrow  for  New  England, 
and  the  Middle  Atlantic  States  with  warmer  weather. 
Clearing  and  fair  weather  is  indicated  for  the  West  Gulf 
States  and  thence  northward  over  the  Upper  Mississippi, 
Missouri  Valleys,  and  Lake  Eegion. 

The  Ohio  Eiver,  Cumberland,  Tennessee,  and  the  Mis- 
sissippi at  St.  Louis,  Cairo,  Vicksburg,  and  New  Orleans, 
will  continue  slowly  falling. 

Cautionary  signals  continue  at  Milwaukee,  Chicago, 
Grand  Haven,  Detroit,  Toledo,  Sandusky,  Cleveland,  Erie, 
and  Buffalo. 

The  lower  map  shows  the  actual  conditions  of  the  weather 
on  the  following  day.  The  area  of  low  barometer,  or  storm- 
centre,  has  moved  eastward  and  the  storm  is  now  central 
over  Western  Pennsylvania  and  the  adjoining  States.  The 
actual  condition  of  the  weather,  showing  the  correctness 
of  the  predictions,  will  be  seen  from  an  inspection  of  the 
following  synopsis  issued  by  the  bureau : 

Synopsis  for  the  Past  Twenty-four  Hours. 

The  severe  storm  which  was  central  in  the  Lower  Mis- 
souri Valley  yesterday  morning  moved  directly  east, 
causing  dangerous  gales  on  the  Lakes  and  general  rains 
in  the  Southern  States,  the  Middle  States,  and  the  Ohio 
Valley.  Snow  and  rain  continue  in  the  Lake  Eegion  this 
morning.  Threatening  weather  is  reported  from  New 
England,  and  colder,  fair  weather  from  the  north-west  and 
south-west.  The  temperature  has  fallen  about  10°  in  the 
Mississippi,  Ohio,  and  Missouri  Valleys  and  Upper  Lake 
Eegion,  with  north  to  west  winds ;  and  it  has  risen  slightly 
in  the  districts  on  the  Atlantic  coast,  with  north-easterly 
winds  in  New  England  and  on  the  Middle  Atlantic  coast, 
and  south-westerly  winds  in  the  South  Atlantic  States. 
The  barometer  is  unusually  low  near  Pittsburg,  and  it  is 
highest  in  Nebraska.  A  light  norther  prevails  on  the 
Texas  coast. 


o5<Kc 


CHAPTER   III. 

Vegetable  and  Animal  Life. 

390.  Vegetation.— The  distribution  of  vegeta- 
tion throughout  the  United  States  is  in  accord- 
ance with  the  distribution  of  the  rainfall.  Four 
characteristic  plant  regions  are  found :  the  Forest, 
the  Prairie,  the  Steppe,  and  the  Pacific  Region. 

391.  The  Forest  Region.— The  chief  requisite 
of  forest  growth— an  abundant  rainfall,  well  dis- 
tributed throughout  the  year  or  during  the  time 
the  trees  are  growing— is  found  especially  in  the 
country  east  of  the  Mississippi,  where  luxuriant 
forests  exist,  unless  removed  by  civilization. 

The  pine,  spruce,  hemlock,  fir,  larch,  juniper, 


and  deciduous  trees,  such  as  the  beech,  maple, 
birch,  alder,  and  poplar,  are  common  in  the 
North. 


Fig.  130.    Scene  in  a  Pine  Woods. 

Deciduous  trees  characterize  the  middle  por- 
tions of  the  forest  region.  In  the  number  and 
variety  of  its  species,  the  oak  is  peculiarly  cha- 
racteristic of  the  middle  part  of  the  forest  region. 

In  the  southern  portion  of  the  forest  region 
evergreen  trees,  such  as  the  live-oak  and  the 
magnolia,  are  characteristic. 


/:-: 


Pig.  131.    Rafting. 


The  forests  have  been  removed,  over  extended 
areas,  from  all  three  parts  of  the  forest  region. 


152 


PHYSICAL    GEOGRAPHY. 


The  cut  logs,  when  the  river-courses  are  suf- 
ficiently large,  are  transported  to  different  sec- 
tions of  the  country  in  huge  rafts. 

392.  The  Prairie  Region. — West  of  the  Mis- 
sissippi Valley,  to  the  Plateau  of  the  Great 
Plains,  the  comparatively  scanty  rainfall  pro- 
duces extensive  prairies,  covered  with  grasses 
and  flowering  herbs.  Forests  are  wanting,  ex- 
cept along  the  river-courses. 

393.  The  Steppe  Region. — From  the  western 
limits  of  the  Great  Plains  to  the  Sierra  Nevada 
and  Cascade  ranges,  lie  the  elevated  plateaus  of 
the  predominant  mountain-system.  Here  the 
rainfall  is  irregular  and  scanty,  and  the  vege- 
tation presents  the  peculiarities  of  a  true  steppe. 
But  few  species  of  plants  occur ;  the  cactus  and 
wild  sage  are  characteristic. 

394.  The  Pacific  Region. — From  the  western 
limits  of  the  steppe  region  to  the  Pacific  coast,  lies 
a  region  whose  features,  in  some  respects,  resemble 
those  of  the  forest  region.  In  Washington  and 
Oregon  dense  forests  of  fir  and  spruce  trees  occur. 
The  cedar,  larch,  maple,  oak,  and  chestnut  are 
common.  In  California  the  periodical  rainfall 
nearly  excludes  the  forest  from  the  valleys  and 
plains ;  but  on  the  mountain-slopes,  where  rains 
are  more  frequent,  well-marked  forests  abound. 
The  pine,  fir,  and  oak  are  characteristic. 

On  the  slopes  of  the  coast  mountains  and  the  Sierra 
Nevada  and  Cascade  Eanges,  dense  forests  of  pine  and  fir 
trees  are  found.  In  some  parts  of  these  regions  the  trees 
frequently  attain  an  immense  size,  many  of  them  exceeding 
300  feet  in  height.  The  largest  are  the  celebrated  "  mam- 
moth trees  of  California,"  a  species  of  pine.  Some  of  these 
trees  are  350  feet  high,  and  have  a  circumference  of  110 
feet  at  the  base.  In  some  of  the  fallen  trees,  the  hollow, 
decayed  trunks  readily  permit  the  passage  of  a  man  and 
horse. 

395.  Animal  Life. — The  large  animals  now 
found  in  the  United  States  are  principally  those 
which  have  been  domesticated,  such  as  the  horse, 
cow,  sheep,  mule,  goat,  and  the  dog. 

In  some  of  the  sparsely-settled  regions  of  the 
East,  and  over  large  areas  in  the  West,  a  few  wild 
animals  are  yet  to  be  found.  In  parts  of  the 
Appalachian  system,  the  black  bear,  panther,  and 
deer  are  found.  The  moose  is  found  in  the  north- 
ern parts  of  the  United  States.  The  immense 
herds  of  buffalo  that  once  roved  over  the  plains 
west  of  the  Mississippi  are  nearly  extinct.  The 
grizzly  bear  and  the  wolf  are  found  on  the  moun- 
tains of  the  Pacific  slope. 

In  the  South,  the  warm,  sluggish  waters  of  the 


lower  courses  of  the  rivers  and  swamps,  harbor 
numerous  alligators. 

A  number  of  species  of  serpents  occur,  but 
only  two,  the  rattlesnake  and  the  copperhead, 
are  venomous. 

The  manatee,  or  sea-cow,  a  curious  herbivorous 
animal  with  paddle-like  legs,  found  in  the  shal- 
low waters  of  the  coast  of  Florida,  sometimes 
attains  a  length  of  ten  feet. 

Some  species  of  the  manatee  in  the  North  Pacific,  off 
Alaska,  reach  thirty  feet  in  length. 

<>0>©<<X, 


CHAPTER  IV. 

\ 

Agricultural  and  Mineral  Produc- 
tions. 

396.  Agricultural  Productions.* — The  princi- 
pal agricultural  productions  of  the  United  States 
are  wheat,  corn,  rye,  oats,  barley,  buckwheat,  hay, 
hops,  potatoes,  flax,  tobacco,  rice,  cotton,  and 
sugar. 

397.  The  Cereals,  wheat,  corn,  rye,  oats,  barley, 
and  buckwheat,  are  grown  principally  north  of  the 
36°  of  north  latitude.  According  to  the  census 
of  1890,  the  States  giving  the  largest  yield  of 
corn  were  Iowa,  Illinois,  and  Kansas,  while  those 
yielding  the  most  wheat  were  Minnesota,  Illinois, 
and  Indiana. 

The  yield  of  corn  is  greater  than  that  of  any  other 
cereal;  the  corn-crop  of  the  year  1890,  in  the  United 


Fig.  132.    Corn-Field, 

States,  amounted  to  1,489,970,000  bushels.     The  wheat- 
crop  of  1890  amounted  to  392,262,000  bushels. 


*  For  Synopsis  of  Census  Reports,  see  Table,  page  171. 


AGRICULTURAL    AND    MINERAL    PRODUCTIONS. 


153 


398.  Tobacco  and  Flax  are  raised  in  large 
quantities  in  various  sections  of  the  country. 

The  principal  tobacco-producing  States  are 
Kentucky,  Virginia,  Pennsylvania,  Ohio,  Ten- 
nessee, and  North  Carolina. 

The  entire  yield  of  tobacco  in  1888  was  565,795,000 
pounds. 


Fig.  133.    Tobacco  Field. 

The  principal  flax-producing  States  are  Minne- 
sota, Iowa,  South  Dakota,  and  Nebraska. 
The  total  value  of  flax-products  in  1889  was  $10,436,228. 

399.  Cotton,  Rice,  and  Sugar  are  cultivated 
mainly  south  of  the  36°  north  latitude. 

The  principal  cotton-producing  States  are 
Texas,  Mississippi,  Alabama,  South  Carolina, 
Georgia,  Arkansas,  and  Louisiana. 


Fig.  134.    Cotton. 
The  cotton-crop  of  the  year  1891  in  the  United  States 


amounted  to  8,655,518  bales,  of  an  average  net  weight 
of  440  pounds  per  bale. 

400.  The  principal  rice-producing  States  are 
South  Carolina,  Louisiana,  Georgia,  and  North 
Carolina.  The  rice-fields  are  confined  to  low,  flat, 
marshy  tracts,  near  the  coast  or  river  bottoms. 


Fig,  135.    Rice  Swamp. 

The  principal  sugar-producing  State  is  Louis- 
iana, the  plantations  being  confined  mainly  to  the 
rich  lands  in  the  neighborhood  of  the  Mississippi 
Delta.  Sugar  is  also  grown  in  South  Carolina, 
Tennessee,  and  Texas. 


Fig,  136.    Sugar-Oane  Field. 

In  1889,  Louisiana  produced  287,490,271  pounds  of  cane- 
sugar. 
More  than  two  million  gallons  of  sorghum  molasses  were 


£54 


PHYSICAL    GEOGRAPHY. 


produced  by  Missouri,  Tennessee,  Kentucky,  Illinois,  and 
Iowa  in  1889. 

Maple-sugar  is  produced  in  Vermont,  New  York,  Ohio, 
New  Hampshire,  Michigan,  and  Indiana.  The  yield  of 
Vermont  in  one  year  was  8,894,302  pounds. 

401.  Mineral  Productions. — The  United  States 
are  particularly  noted  for  the  richness  and  variety 
of  their  mineral  deposits.  Nearly  all  the  import- 
ant metals  are  found  in  various  portions  of  the 
country,  some  of  the  deposits  extending  over 
ureas  of  enormous  extent. 

402.  Precious  Metals. — Gold,  silver,  and  plati- 
num occur.  The  deposits  of  gold  and  silver  are 
large. 

Gold. — The  principal  deposits  of  gold  occur 
in  the  mountainous  districts  in  the  eastern  and 
western  portions  of  the  country.  The  Californian 
region,  which  embraces  the  entire  western  coast 
and  much  of  the  country  as  far  east  as  the  Great 
Plains,  is  the  richest.  The  deposits  are  especially 
valuable  in  the  basins  of  the  Sacramento  and  San 
Joaquin  Rivers.  Gold  is  found  either  in  quartz 
veins  or  in  alluvial'deposits. 

Silver  is  found  either  in  the  gold-fields  already 
mentioned,  or  in  deposits  of  galena,  one  of  the 
most  valuable  ores  of  lead.  It  also  occurs  pure 
or  native  in  the  copper  regions  of  Lakes  Superior 
and  Michigan. 

Platinum  has  been  found  in  small  quantities 
in  both  the  eastern  and  western  portions  of  the 
country. 

403.  Ordinary  Metals. — Iron,  copper,  zinc,  and 
lead  occur  in  various  portions  of  the  eastern,  cen- 
tral, and  western  sections  of  the  country. 

Iron,  which  intrinsically  is  the  most  valuable 
of  all  the  metals,  is,  perhaps,  the  most  widely 
distributed.  Valuable  deposits  of  various  iron 
ores,  mainly  oxides  and  carbonates,  occur  in 
many  parts  of  the  country.  The  deposits  are  ex- 
ceedingly rich  in  Northern  Michigan  and  Wis- 
consin ;  in  the  neighborhood  of  the  Adirondacks 
in  New  York;  in  Pennsylvania;  in  Missouri, 
where  the  deposits  at  one  time  actually  formed 
two  mountains  of  iron ;  in  the  district  of  Lake 
Superior;  in  Alabama,  and  elsewhere.  The  de- 
posits in  Pennsylvania  are  the  most  valuable,  from 
their  vicinity  to  beds  of  coal  and  limestone,  which 
are  necessary  for  the  reduction  of  the  ore. 

Copper  occurs  in  large  quantities  in  the  east- 
ern, western,  and  central  sections  of  the  country. 
The  ores  are  principally  sulphides  or  oxides,  or 
the  native  or  metallic  copper.  The  most  valu- 
able deposits  are  found  in  the  neighborhood  of 


Keweenaw  Point,  Lake  Superior,  where  large 
beds  of  the  native  material  occur. 

Zinc. — The  most  valuable  deposits  are  found  in 
Missouri,  Wisconsin,  and  Kansas.  It  also  occurs 
in  the  Atlantic  States,  from'  Maine  to  Virginia. 

Lead. — Valuable  deposits  are  found  in  the  East, 
from  Maine  to  North  Carolina.  The  largest  and 
richest  districts,  however,  are  in  the  interior,  in 
Colorado  and  Utah,  where  it  occurs  with  silver, 
and  in  the  Mississippi  Valley ;  in  Wisconsin, 
Iowa,  Illinois,  and  Missouri. 

404.  Among  other  valuable  metals,  tin,  mer- 
cury, chromium,  nickel,  cobalt,  antimony,  bis- 
muth, manganese,  are  found  in  small  quantities. 

Tin  occurs  in  limited  quantities  both  in  the  East 
and  in  the  West.  So  far  as  is  known,  the  deposits 
are  richest  in  the  Black  Hills  in  Dakota. 

Mercury  is  found  either  pure  or  in  combina- 
tion. The  principal  ore  is  the  sulphide  of  mer- 
cury or  cinnabar.  The  deposits  in  California  are 
the  most  important. 

Chromium  is  found  in  moderately  large  quan- 
tities in  various  portions  of  the  Atlantic  States, 
as  far  south  as  Virginia. 

Nickel,  cobalt,  antimony,  bismuth,  and  man- 
ganese are  found  in  limited  quantities. 

405.  Coal,— The  coal-fields  of  the  United  States 
are  the  richest  in  the  world.  Immense  deposits 
occur  in  the  eastern,  central,  and  western  sections 
of  the  country.     So  far  as  is  known,  the  eastern 


Fig.  137.    Coal-Mine. 

coal-field,  which  covers  portions  of  Pennsylvania, 
Ohio,  Virginia,  Kentucky,  Tennessee,  and  Ala- 
bama, is  the  most  extensive. 


AGRICULTURAL    AND    MINERAL    PRODUCTIONS. 


155 


Other  coal-fields  occur  in  Illinois  and  Missouri, 
in  Texas,  Michigan,  Rhode  Island,  and  New 
Brunswick  and  Nova  Scotia. 

The  area  of  the  coal-fields  of  Western  Europe  is  estimated 
by  Dana  at  about  20,000  square  miles,  while  the  total  area 
of  those  of  the  United  States  probably  exceeds  125,000 
square  miles.  In  the  United  States,  Pennsylvania  possesses 
the  most  extensive  and  the  richest  deposits,  the  total  area 
of  the  deposits  in  this  State  being  nearly  20,000  square 
miles,  or  equal  to  those  of  Western  Europe.  The  richness 
of  the  American  coal-fields  cannot  fail  to  exert  an  import- 
ant influence  on  the  future  development  of  the  country. 

406.  Peat-Bogs  of  Massachusetts. — Peat  con- 
sists of  a  black,  carbonaceous  deposit  which  ac- 
cumulates in  badly-drained  regions  of  humid 
climates.  The  surfaces  of  the  peat-marshes  are 
often  covered  with  a  thin  crust,  formed  by  the 
interlacing  roots  of  vegetable  growths.  Below 
this  crust  is  a  treacherous,  oozy  quagmire. 

When  peat  is  dried  it  is  suitable  for  fuel. 
Dana  estimates  that  Massachusetts  contains  fifteen 
billion  cubic  feet  of  peat.  Large  deposits  occur  in 
the  Great  Dismal  Swamp,  in  North  Carolina  and 
Virginia. 

407.  Petroleum,  or  Coal  Oil,  is  found  in  various 


Fig.  138.    Oil  Well  and  Tank. 

sections.  The  most  valuable  deposits  occur  in  a 
region  embracing  Western  Pennsylvania,  Vir- 
ginia, Ohio,  and  Michigan.  Petroleum  is  found 
also  in  the  West. 


The  oil  is  obtained  by  boring.  The  wells  so 
produced  are  similar  to  artesian  wells,  except  in 
the  material  discharged.  In  many  instances  the 
oil  issues  in  powerful  streams,  which  continue  to 
flow  for  considerable  periods.  The  crude  oil  is 
generally  stored  in  huge  tanks,  from  which  it  is 
transferred  to  barrels  or  iron  tanks  for  trans- 
portation. Much  is  also  distributed  for  great  dis 
tances  through  lines  of  pipes  called  pipe-lines. 
For  most  commercial  uses  it  is  necessary  to  re- 
fine or  purify  the  oil. 

408.  Natural  Gas. — Accumulations"  of  natural 
or  rock-gas  occur  in  nearly  all  portions  of  the 
United  States,  but  such  deposits  are  especially 
rich  in  the  regions  where  coal  oil  is  found. 
Western  Pennsylvania,  and  the  adjoining  States, 
yield  great  quantities  of  such  gas. 

The  gas  is  obtained  by  borings  similar  to  those 
made  for  artesian  wells  or  coal-oil  wells.  From 
the  gas  wells  thus  formed  the  gas  issues  forth  with 
great  velocity.  When  lighted  it  burns  with  a 
flame  similar  to  that  of  ordinary  illuminating 
gas.  Like  ordinary  gas  it  burns  with  a  pale 
bluish  flame  when  mixed  with  air,  and  affords 
an  excellent  source  of  artificial  heat. 

Natural  gas  has  been  known  for  many  years  past,  but  it 
is  only  recently  that  its  great  extent  and  quantity  have 
been  ascertained.  In  many  districts — notably  in  the  city 
of  Pittsburgh  and  vicinity — natural  gas  has  practically 
superseded  illuminating  gas  as  a  source  of  light,  and  has 
almost  entirely  replaced  ordinary  coal  as  a  source  of  heat. 
The  value  of  such  a  natural  product  in  any  manufacturing 
centre  can  scarcely  be  overestimated,  and  its  successful  in- 
troduction in  any  locality  has  in  all  cases  been  attended 
with  a  marked  growth  in  the  extent  and  variety  of  its 
manufactures.  Although  such  deposits  must  in  perhaps  a 
comparatively  short  time  become  exhausted,  as  yet  they 
show  but  little  signs  of  failure. 

The  gas  escapes  from  the  well  under  great  pressure. 
Before  its  delivery  to  consumers,  through  pipes  like  ordi- 
nary gas-pipes,  the  pressure  is  reduced  by  suitable  contri- 
vances ;  so  that  its  consumption  is  not  attended  with  any 
greater  risk  than  that  attending  ordinary  illuminating  gas. 

409.  Salt. — Beds  of  rock-salt  occur  in  Louisi- 
ana, Virginia,  and  in  various  parts  of  the  West. 
Larg*e  quantities  are  obtained  by  evaporating  the 
waters  of  saline  or  brine  springs.  These  are  of 
common  occurrence.  The  most  valuable  are 
found  in  New  York,  in  the  neighborhood  of 
Salina  and  Syracuse ;  in  Virginia,  Michigan,  Ken- 
tucky, and  in  the  Far  West. 

410.  Building  Stones. — Large  deposits  of  valu- 
able building  stones  are  found  in  all  parts  of  the 
country.  Among  the  most  common  are  various 
kinds  of  sandstone,  marble,  granite,  slate,  mag- 
nesian   limestone,   serpentine,   gneiss,   and    mica 


156 


PHYSICAL    GEOGRAPHY. 


sclrst.     Valuable   deposits   of  clay  occur,  from 
which  excellent  bricks  are  made. 


oX^c 


CHAPTER  V. 

Alaska. 

411.  Extent  of  Territory. — The  Territory  of 
Alaska,  now  a  part  of  the  domain  of  the  United 
States,  embraces  the  north-western  part  of  the 
North  American  Continent,  and  extends  south 
from  the  shores  of  the  Arctic  Ocean  to  about  54° 
of  N.  lat.  The  main  part  of  the  Territory  lies  west 
of  the  141°  E.  long,  from  Greenwich.  South  of 
Mt.  St.  Elias,  however,  it  embraces  a  narrow 
strip  extending  south-eastwardly  along  the  coast 
of  British  Columbia. 

The  Territory  of  Alaska  embraces  an  area  of 
about  530,000  miles,  or,  approximately,  about 
one-sixth  of  the  whole  area  of  the  remainder  of 
the  domain  of  the  United  States.  This  country 
was  purchased  from  Russia  by  the  United  States 
in  1867,  at  a  cost  of  $7,200,000. 

Indentations  of  the  Coast. — The  coast-line  of 
Alaska  is  exceedingly  irregular,  its  entire  length 
amounting  to  as  much  as  8000  miles.  The  shores 
of  the  Arctic  are  the  least  indented.  The  western 
and  southern  coasts  are  deeply  indented. 

Behring  Sea  and  Straits  separate  Alaska  from 
Asia.  The  Pacific  Ocean  enters  the  wide  curve 
of  the  southern  coast  as  the  Gulf  of  Alaska. 
Smaller  indentations  on  the  western  coasts  are 
found  in  Norton  Sound,  Kuskovitch  Bay,  Bristol 
Bay,  and  in  the  numerous  bays  and  inlets  on  the 
southern  coasts,  in  which  true  fiords  occur. 

412.  Islands.  —  Numerous  islands  lie  off  the 
western  and  southern  coasts.  The  principal  of 
these  are  St.  Lawrence  Island  and  Nunivak,  on 
the  western  coast ;  the  Aleutian  Islands,  which  ex- 
tend in  a  curve  from  the  Alaskan  Peniftsula 
nearly  to  Kamtchatka;  Afognak  and  Kadiak 
islands,  off  the  southern  shores  of  the  peninsula; 
and  Baranoff,  Chichagof  and  Prince  of  Wales 
islands  off  the  south-eastern  shores. 

413.  Surface  Structure. — The  northern  portions 
of  Alaska  are  low  and  flat,  and  the  plains,  drained 
by  a  few  small,  sluggish  streams,  are,  for  the  most 
part,  frozen  moor-lands,  similar  to  the  tundras  of 
Northern  Siberia.  They  form  a  dreary,  desolate 
country,  for  the  greater  part  unexplored,  covered 


during  the  brief   summer  by   a   comparatively 
dense  growth  of  grasses. 

The  rest  of  Alaska  is  generally  mountain- 
ous, being  traversed  by  prolongations  of  the 
Pacific  Mountain-System.  The  highest  eleva- 
tions are  those  of  the  south-eastern  coast,  Mt.  St. 
Elias  being  19,500  feet  above  the  level  of  the 
sea.  Mts.  Crillon  and  Fairweather  are  scarcely 
inferior  in  height.  These  mountains  contain  nu- 
merous glaciers  which  descend  nearly  to  the  level 
of  the  sea.  The  chain  of  the  Aleutian  Islands 
is  mountainous,  and,  like  the  mountains  of  the 
south-western  coast,  contains  many  volcanic 
peaks. 

414.  Drainage  System. — The  principal  river 
of  Alaska  is  the  Yukon,  which,  so  far  as  known, 
has  a  length  of  at  least  2000  miles.  It  is  one  of 
the  largest  rivers  in  North  America,  so  far  as 
the  volume  of  its  discharge  is  concerned,  which 
appears  to  be  as  great  as  that  of  the  Missis- 
sippi. In  some  portions  of  its  lower  course  it 
is,  in  places,  20  miles  wide.  An  extensive  delta 
formation  occurs  at  the  mouth  of  the  river.  The 
Lewis  and  the  White,  its  principal  tributaries,  are 
situated  near  the  head-waters  of  the  Yukon,  in 
the  Dominion  of  Canada. 

The  Kuskovim  is  the  only  other  important 
river.  Unlike  the  delta-mouth  of  the  Yukon, 
the  Kuskovim  discharges  its  waters  into  Behr- 
ing Sea  through  a  wide  estuary.  The  spring  tides 
sometimes  rise  in  this  estuary  to  the  height  of  over 
50  feet. 

The  glaciers  of  the  south-eastern  coast  feed  a 
number  of  lakes,  so  near  together  as  to  permit 
the  establishment  of  portage-routes  of  travel. 

415.  Climate. — The  climate  of  Alaska  is,  gen- 
erally, cold  and  wet,  although  the  influence  of 
the  Japan  Current,  and  the  westerly  winds  and 
rain,  render  the  mean  annual  temperature  much 
warmer  than  corresponding  latitudes  in  the  inte- 
rior, or  even  on  the  eastern  coasts  of  the  North 
American  Continent.  Fogs  and  rains  are  fre- 
quent. The  annual  rainfall  at  Sitka,  on  Baranoff 
Island,  is  about  85  inches. 

416.  Vegetation. — Dense  grasses  cover  por- 
tions of  the  tundras,  river  valleys,  and  hillsides 
during  the  brief  summer.  The  wet  climate,  how- 
ever, renders  the  curing  of  hay  a  difficult  matter, 
and,  consequently,  the  rearing  of  cattle  is  attended 
with  difficulty. 

Portions  of  the  lower  mountainous  slopes  and 
river  valleys  are  covered  with  forests  of  yellow 
cedar  and  spruce.     In  the  greater  part  of  the 


SYLLABUS. 


157 


Territory  no  timber  grows  at  an  altitude  greater 
than  1000  feet  above  the  sea.  Turnips,  potatoes, 
and  radishes  have  been  cultivated  in  southern 
portions  of  the  Territory  with  fair  success. 

417.  Animal  Life. — The  rivers  are  visited  dur- 
ing the  breeding  season  by  myriads  of  salmon. 
This  fish  forms  the  principal  food  of  the  inhabit- 
ants, who,  at  the  beginning  of  the  season,  desert 
the  interior  for  the  banks  of  the  rivers.  Halibut, 
herring,  codfish,  and  mackerel,  are  caught  off  the 
coasts  of  the  Territory . 

The  fur  seal,  the  walrus,  and  the  sea-otter  are 
caught  in  great  numbers  for  their  valuable  fur. 
The  whale  is  found  in  the  Arctic  waters  of  the 
northern  coast.  The  polar  bear,  the  brown  bear, 
the  mink,  the  black  or  silver  fox,  the  moose,  and 


the  reindeer  are  also  found  in  the  Territory. 
Dense  swarms  of  bloodthirsty  mosquitoes  and 
black  flies  occur  in  nearly  all  parts  of  the 
country. 

418.  Minerals. — Beds  of  coal  of  an  inferior 
quality  have  been  discovered  in  various  parts 
of  the  country.  Deposits  of  silver,  gold,  cop- 
per, lead,  and  cinnabar  also  occur. 

419.  Inhabitants. — The  inhabitants  of  Alaska 
consist  principally  of  the  Esquimaux  or  Innuit, 
the  Indians,  and  the  Aleuts,  or  the  inhabitants 
of  the  Aleutian  Islands,  the  Creoles  or  Russian 
half-breeds,  and  the  inhabitants  of  the  remaining 
archipelagoes,  together  with  a  few  whites. 

Sitka,  on  Baranoff  Island,  is  the  principal  set- 
tlement. 


— ^-S-e^fij^LS^^^ 


SYLLABUS. 


-<K>J*JC 


The  area  of  the  United  States,  exclusive  of  Alaska,  is 
about  3,000,000  square  miles. 

The  coast  line  is  comparatively  simple  and  unbroken. 
The  principal  indentations  on  the  east  are  Long  Island 
Sound,  Delaware  and  Chesapeake  Bays,  and  Albemarle  and 
Pamlico  Sounds ;  on  the  west,  the  Gulf  of  Georgia  and  the 
Bay  of  San  Francisco. 

The  slope  of  the  Atlantic  shores  is  gradual ;  that  of  the 
Pacific  shores  is  abrupt. 

On  the  Atlantic  coast,  the  islands  north  of  Cape  Cod  are 
for  the  most  part  rocky ;  those  south  of  Cape  Cod  are  gen- 
erally low  and  sandy. 

Mangrove  islands  are  formed  by  sediment  collecting 
around  the  closely  intertwined  roots  of  mangrove  trees. 
These  islands  occur  in  the  shallow  waters  off  the  coast  of 
Florida. 

Nearly  all  of  Florida,  south  of  the  Everglades,  and 
probably  as  far  north  on  the  eastern  coast  as  St.  Augus- 
tine, consists  of  a  peculiar  variety  of  coral  formation. 

The  Pacific  system  is  the  predominant  mountain-system ; 
the  Appalachian  system  is  the  secondary  system. 

The  Pacific  system  consists  of  the  Rocky  Mountains,  the 
Sierra  Nevada,  the  Cascade,  and  the  Coast  Mountains. 

The  highest  peaks  are  found  in  the  Cascade  Mountains. 

Portions  of  the  Pacific  Mountain  ranges  contain  extinct 
volcanoes. 

The  Appalachian  system,  or  the  system  of  the  Allegha- 
nies,  includes  the  White  Mountains,  the  Green  Mountains, 
the  Adirondacks,  the  Catskills,  the  Blue  Ridge,  and  the 
Cumberland  Mountains. 

There  are  two  great  low  plains  in  the  United  States  :  the 
Atlantic  Coast  Plain  and  the  Plain  of  the  Mississippi 
Valley. 

The  principal  rivers  draining  into  the  Atlantic  Ocean 
are  the  Penobscot,  Merrimac,  Connecticut,  Hudson,  Dela- 
ware, Susquehanna,  Roanoke,  Cape  Fear,  Santee,  Savan- 
nah, Altamaha,  and  St.  John's. 
18 


The  principal  rivers  draining  into  the  Mexican  Gulf  are 
the  Appalachicola,  Alabama,  Mississippi,  Sabine,  Trinity, 
Brazos,  Colorado,  and  the  Rio  Grande. 

The  principal  rivers  draining  into  the  Pacific  Ocean  are 
the  Columbia,  Sacramento,  San  Joaquin,  and  the  Colorado. 

The  Great  Basin,  between  the  Wahsatch  and  the  Sierra 
Nevada  Mountains,  has  an  inland  drainage. 

Soda  Valley,  in  Southern  California,  and  Death  Valley, 
in  Eastern  California,  are  below  the  level  of  the  sea. 

The  Great  Lakes,  Superior,  Michigan,  Huron,  Erie,  and 
Ontario,  form  the  largest  system  of  fresh-water  lakes  in 
the  world. 

The  United  States  extends  from  the  isotherm  of  40°  Fahr. 
to  77°  Fahr.,  and  therefore  lies  in  the  physical  north  tem- 
perate and  the-  torrid  zones. 

A  marked  contrast  exists  between  the  temperature  of 
the  eastern  and  the  western  coasts  of  the  northern  half 
of  the  country.  The  eastern  coasts  are  colder  than  the 
western. 

The  greater  warmth  of  the  western  coasts  is  caused  by 
warm  ocean  currents,  westerly  winds,  and  heavy  rainfalls. 

The  Atlantic  seaboard  is  colder  than  corresponding  lati- 
tudes on  the  western  shores  of  Europe  or  on  the  western 
shores  of  the  United  States. 

From  observations  dating  back  to  the  year  1738  it  ap- 
pears that  from  that  time  the  climate  of  the  United  States 
has  undergone  no  decided  change. 

The  United  States  lies  in  the  zone  of  the  variable  winds; 
westerly  winds  predominate. 

The  heaviest  annual  rainfall  is  65  inches.  It  occurs  near 
the  borders  of  the  Gulf  States  and  along  the  Pacific  sea- 
board in  Washington  and  Oregon.  The  smallest  annual 
rainfall  is  found  in  the  Great  Basin ,  it  varies  from  5  to  10 
inches.  East  of  the  100th  meridian  from  Greenwich  the 
average  fall  is  40  inches. 

On  the  Atlantic  coast  rain  is  especially  abundant  during 
spring ;  on  most  of  the  Pacific  coast,  during  winter. 


158 


PHYSICAL    GEOGRAPHY. 


The  Weather  Bureau  was  established  for  the  observation 
of  the  meteorological  conditions  of  the  country. 

There  are  four  characteristic  plant  regions  in  the 
United  States:  the  Forest,  the  Prairie,  the  Steppe,  and 
the  Pacific. 

The  forest  region  lies  mainly  east  of  the  Mississippi ;  the 
characteristic  trees  are  the  pine,  spruce,  hemlock,  fir,  juni- 
per, beech,  maple,  birch,  alder,  oak,  and  poplar. 

The  principal  large  animals  of  the  United  States  are 
those  which  have  been  domesticated,  as  the  horse,  ox, 
cow,  sheep,  mule,  goat,  and  dog. 

Among  wild  animals  are  the  black  bear,  panther,  deer, 
grizzly  bear,  wolf,  and  manatee  or  sea-cow. 

The  principal  agricultural  productions  are  wheat,  corn, 
rye,  oats,  barley,  buckwheat,  hay,  hops,  flax,  tobacco,  rice, 
cotton,  and  sugar. 

.  The  principal  metals  are  gold,  silver,  platinum,  iron, 
copper,  zinc,  lead,  tin,  mercury,  chromium,  nickel,  cobalt, 
antimony,  bismuth,  and  manganese. 

Deposits  of  coal,  rock-salt,  marble,  coal  oil,  and  natural 
gas  are  found,  and  many  varieties  of  durable  building- 
stone. 

Extensive  peat-bogs  occur  in  Massachusetts  and  Virginia. 

The  Territory  of  Alaska  has  an  area  of  about  530,000 
square  miles  and  is  nearly  one-sixth  that  of  the  area  of  the 
rest  of  the  domain  of  the  United  States. 

The  coast  line  of  Alaska  is  very  irregular,  and  has  a 
length  of  at  least  8000  miles. 

Behring  Sea  on  the  west,  and  the  Gulf  of  Alaska  on  the 
south,  are  the  principal  indentations  of  the  coast.  Norton 
Sound  and  Kuskovitch  and  Bristol  Bays  are  among  the 
most  important  of  the  smaller  indentations. 

The  principal  islands  are  St.  Lawrence  Island,  Nunivak, 


the  Aleutian  Islands,  Afognak,  Kadiak,  Baranoff,  Chicha- 
gof,  and  Prince  of  Wales. 

The  northern  portions  of  Alaska  are  low  and  flat,  and 
are  covered  by  tundras  or  frozen  moor-lands.  The  rest  of 
the  country  is  generally  mountainous,  and  is  traversed  by 
prolongations  of  the  Pacific  Mountain  system  of  North 
America.  Mts.  St.  Elias,  Fairweather,  and  Crillon  are 
the  principal  peaks. 

The  principal  river  of  Alaska  is  the  Yukon,  which  is 
some  2000  miles  long,  and  is  one  of  the  largest  rivers  of 
the  North  American  Continent.  The  Kuskovim  is  the 
only  other  important  river.  The  Yukon  has  a  delta 
mouth — the  Kuskovim,  an  estuary. 

The  climate  of  Alaska  is  cold  and  wet,  though,  under 
the  combined  influences  of  the  Japan  current,  the  rains, 
and  the  warm  south-westerly  winds,  the  climate  is  less 
severe  than  at  corresponding  latitudes  in  the  interior,  or 
on  the  Atlantic  coast. 

Dense  growths  of  grasses  abound  during  the  brief  sum- 
mer.   Forests  of  yellow  cedar  and  spruce  occur. 

The  chief  animals  are  the  polar  and  brown  bears,  the 
mink,  black  or  silver  fox,  the  moose,  and  the  reindeer. 
The  whale  is  found  in  the  waters  off  the  northern  shores, 
and  the  walrus,  the  seal,  and  the  sea-otter  are  sources 
of  wealth  by  reason  of  their  valuable  furs.  Salmon,  hali- 
but, cod,  and  herring,  are  the  principal  food-fish. 

Deposits  of  coal,  silver,  gold,  lead,  and  cinnabar  occur  in 
different  parts  of  the  country. 

The  inhabitants  consist  of  various  elements,  the  princi- 
pal of  which  are  the  Esquimaux,  the  Indians,  the  Aleuts, 
the  Creoles,  and  the  people  of  the  archipelagoes  of  the 
southern  and  south-eastern  coast. 

Sitka,  on  Baranoff  Island,  is  the  principal  settlement. 


REVIEW  QUESTIONS. 


oJO{c 


State  the  geographical  position  of  the  United  States. 

Describe  the  peculiarities  of  its  coast  lines. 

Name  the  principal  indentations  of  the  eastern  coast. 
Of  the  western  coast. 

In  what  respect  do  the  islands  which  lie  north  of  Cape 
Cod  differ  from  those  which  lie  south  of  it? 

What  is  the  origin  of  the  islands  off  the  southern  coast 
of  Florida? 

Describe  the  Pacific  Mountain  system.  Locate  the  Great 
Plains.    The  Great  Basin. 

Describe  the  Appalachian  Mountain  system. 

Name  the  great  low  plains  of  the  United  States. 

Name  the  important  rivers  which  drain  directly  into 
the  Atlantic ;  name  those  which  drain  into  the  Atlantic 
through  the  Gulf  of  Mexico ;  name  those  which  drain  into 
the  Pacific. 

What  system  of  inland  drainage  is  found  in  the  United 
States? 

Describe  the  lake-systems  of  the  United  States. 

In  what  mathematical  zone  is  the  United  States  situated  ? 
In  what  physical  zones? 

Between  what  isothermal  lines  does  the  United  States 
extend  ? 

Describe  the  general  direction  of  the  isotherm  of  40° 
Fahr.     Of  55°  Fahr.     Of  60°  Fahr. 

What  difference  exists  between  the  climate  of  the  eastern 
and  western  coasts  ?  What  are  the  causes  of  this  difference  ? 


Has  the  climate  of  the  United  States  undergone  any  de- 
cided change  during  the  last  hundred  years  ? 

In  what  wind  zone  does  the  United  States  lie? 

In  what  parts  of  the  country  does  the  heaviest  annual 
rainfall  occur?    The  smallest  annual  rainfall? 

What  is  the  rainfall  of  the  upper  Mississippi  Valley? 
Of  the  lower  Mississippi  ? 

At  what  season  of  the  year  do  the  heaviest  rains  occur 
on  the  Atlantic  coast  ?    On  the  Pacific  coast  ? 

For  what  was  the  Weather  Bureau  established  ? 

What  are  tornadoes  ? 

Under  what  four  characteristic  plant  regions  may  the 
vegetation  of  the  United  States  be  arranged? 

Describe  the  location  of  each  of  these  regions. 

Name  the  principal  forest  trees  of  the  United  States. 

Name  the  principal  domesticated  and  wild  animals  of 
the  United  States. 

Enumerate  the  principal  agricultural  productions. 

Name  the  principal  corn-producing  States.  The  prin- 
cipal wheat-producing  States. 

Name  the  principal  cotton-producing  States.  The  prin- 
cipal rice-producing  States.  The  principal  sugar-producing 
States. 

What  valuable  metals  are  found  in  the  United  States? 

What  other  valuable  mineral  substances  occur? 

What  are  the  limits  of  the  Territory  of  Alaska?  State 
its  boundaries.    What  is  its  area? 


What  sum  was  paid  for  Alaska  by  the  United  States 
Government  ? 

Name  the  principal  indentations  of  the  coast  of  Alaska. 
What  is  the  extent  of  its  coast  line  ? 

Name  the  principal  islands  of  the  western  coast.  Of  the 
southern  coast. 

Describe  the  surface  structure  of  Alaska.  To  what  gen- 
eral system  of  mountains  do  its  elevations  belong?  Name 
some  of  the  principal  peaks.     Are  any  of  them  volcanic? 

Describe  the  river-system  of  the  Yukon.  Where  is  the 
Kuskovim  Eiver?  Which  of  these  rivers  has  a  delta 
mouth?    Which  has  an  estuary? 


What  is  the  general  climate  of  Alaska  ?  How  does  the 
climate  compare  with  that  of  corresponding  latitudes  in 
the  interior  of  the  country  or  on  the  Atlantic  coast  ?  Why 
is  this  ? 

Describe  the  vegetation  of  Alaska.  What  are  the  prin- 
cipal trees? 

Name  the  principal  food-fish  of  Alaska.  Name  the  prin- 
cipal fur-bearing  animals.  What  other  large  animals  are 
found  in  the  country  ? 

Which  is  the  principal  settlement?  Name  some  of  the 
different  people  who  inhabit  Alaska. 


MAP   QUESTIONS. 


°*Kc 


Describe  from  the  Physical  Map  of  the  United  States 
the  surface  structure  of  the  country,  giving  the  relative 
position  of  the  High  Lands  and  Low  Lands. 

Describe  the  Pacific  Mountain  System. 

Describe  the  Appalachian  Mountain  System. 

Locate  the  following :  the  Black  Hills ;  the  Wahsatch 
Mountains ;  the  Sierra  Madre ;  San  Louis  Park ;  Pike's 
Peak ;  Long's  Peak ;  Fremont's  Peak. 

Describe  the  drainage  of  the  Great  Lakes. 

Name  the  principal  rivers  which  empty  into  the  Atlantic. 
Into  the  Gulf  of  Mexico.     Into  the  Pacific. 

Name  the  principal  tributaries  of  the  Mississippi. 

Where  are  the  Santa  Barbara  Islands?  The  Bahama 
Islands?    Vancouver's  Island? 


Trace  on  the  map  the  isothermal  line  of  45°. 

What  is  the  cause  of  the  southward  deflection  of 
the  isothermal  lines  'in  the  western  part  of  the  United 
States  ? 

Prove  from  the  isotherms  that  the  climate  of  the 
northern  half  of  the  Atlantic  coast  is  colder  than  the 
southern  half. 

In  what  portions  of* the  United  States  is  the  lowest  mean 
annual  temperature  found?    The  highest? 

Name  the  swamps  and  sounds  of  the  Atlantic  sea- 
board whose  formation  is  to  be  traced  to  fluvio-marine 
deposits. 

What  swamp  is  due  to  coral  formations? 


*HSH« 


GENERAL    SYLLABUS. 


>j<«o< 


Physical  Geography  treats  of  the  distribution  of  the  land, 
water,  air,  animals,  and  plants  of  the  earth. 

The  earth  moves  through  empty  space  around  the  sun. 
It  is  kept  in  motion  in  its  orbit  by  its  inertia  and  the 
attraction  of  the  sun. 

The  rotundity  of  the  earth  is  proved — 1.  By  the  ap- 
pearance of  approaching  or  receding  objects ;  2.  By  the  cir- 
cular shape  of  the  horizon ;  3.  By  the  shape  of  the  earth's 
shadow ;  4.  By  the  great  circle  of  illumination ;  5.  By 
actual  measurement. 

Exact  geographical  position  is  determined  by  reference 
to  certain  imaginary  lines  called  parallels  and  meridians. 

Representations  of  the  whole  or  of  parts  of  the  earth's 
surface  are  made  by  means  of  maps. 

Maps  are  drawn  on  different  projections :  the  Equa- 
torial, the  Polar,  and  Mercator's  projection  are  in  the  most 
general  use. 

The  length  of  daylight  in  either  hemisphere  depends  on 
the  extent  to  which  that  hemisphere  is  inclined  towards 
the  sun ;  the  longest  day  in  the  northern  hemisphere  occur- 
ring June  21st,  when  the  sun  is  vertical  over  the  Tropic  of 
Cancer. 

The  change  of  seasons  is  occasioned  by  the  revolution 
of  the  earth,  together  with  the  inclination  of  the  earth's 
axis  at  an  angle   of  66°   33'  to   the  plane  of  its  orbit, 


and  the  constant  parallelism  of  the  axis  with  any  former 
position. 

The  Torrid  Zone  is  the  hottest  part  of  the  earth,  because, 
at  one  time  or  another  throughout  the  year,  every  part  of 
its  surface  receives  the  vertical  rays  of  the  sun. 

The  following  different  opinions  are  held  concerning  the 
condition  of  the  interior  of  the  earth : 

(1.)  That  the  earth  has  a  solid  centre  and  crust,  with  a 
neated  layer  between. 

(2.)  That  the  crust  only  is  solid,  and  the  remainder  suf- 
ficiently heated  to  be  in  a  fused  or  pasty  condition. 

(3.)  That  the  earth  is  solid  throughout,  but  highly  heated 
in  the  interior. 

The  proofs  of  the  present  highly-heated  condition  of 
the  interior  of  the  earth  are  as  follows : 

1.  In  all  parts  of  the  earth,  the  deeper  we  penetrate  the 
crust,  the  higher  the  temperature  becomes ;  that  is  t©  say, 
the  entire  interior  is  heated. 

2.  The  presence  of  volcanoes,  which,  in  all  latitudes, 
eject  melted  rock  from  the  inside  of  the  earth  ;  that  is  to 
say,  the  entire  interior  is  filled  with  matter  sufficiently  hot 
to  melt  rock  at  ordinary  pressures. 

3.  The  occurrence  of  earthquake  shocks  in  all  parts  of 
the  earth. 


160 


PHYSICAL    GEOGRAPHY. 


The  original  fluidity  of  the  earth  is  rendered  probable  by 
the  following  circumstances : 

(1.)  By  the  spherical  shape  of  the  earth. 
(2.)  The  crystalline  rocks,  or  those  formed  in  the  presence 
of  great  heat,  underlying  all  others. 

(3.)  The  warmer  climate  of  the  earth  during  the  geolog- 
ical past. 

Volcanoes  eject  from  the  interior  of  the  earth — 1. 
Melted  rock  or  lava;  2.  Showers  of  ashes  or  cinders;  3. 
Vapors  or  gases. 

These  materials  are  brought  up  from  great  depths  into 
the  volcanic  mountain  by  the  force  caused  by  a  contract- 
ing globe.  They  may  escape  from  the  crater — 1.  By  the 
pressure  of  highly-heated  vapors;  2.  By  the  pressure 
exerted  by  a  column  of  liquid  lava. 

All  volcanoes  are  found  near  the  coasts  of  the  continents, 
or  on  islands. 

The  movements  of  the  earth's  crust  produced  by  earth- 
quake shocks  are — 1.  A  wave-like  motion  around  the 
centre  of  disturbance ;  2.  An  upward  motion  ;  3.  A  rotary 
motion. 

The  following  facts  have  been  discovered  as  regards 
earthquakes : 

(1.)  Their  place  of  origin  is  not  very  deep  seated. 

(2.)  The  area  of  disturbance  increases  with  the  energy 
of  the  shock  and  the  depth  of  its  origin. 

(3.)  The  shape  of  its  origin  is  that  of  a  line  and  not 
that  of  a  point. 

(4.)  The  shape  of  the  area  of  disturbance  varies  with 
the  elasticity  of  the  materials  through  which  the  shock 
moves. 

(5.)  The  earthquake  motion  travels  as  spherical  waves, 
which  move  outward  in  all  directions  from  their  point 
of  origin. 

The  most  violent  earthquake  shocks  continue  but  for  a 
short  time. 

Earthquakes  are  generally  caused  by  the  strain  produced 
by  the  contraction  of  the  crust. 

Earthquake  shocks  are  of  more  frequent  occurrence — 1. 
In  winter  than  in  summer ;  2.  At  night  than  during  the 
day ;  3.  During  the  new  and  full  moon,  than  during  any 
other  phase. 

Earthquake  shocks  may  occur  in  any  part  of  the  world, 
but  are  of  most  frequent  occurrence  in  the  neighborhood 
of  volcanoes. 

Bocks  may  be  divided,  according  to  their  origin,  into  three 
classes:  1.  Igneous;  2.  Aqueous;  3.  Metamorphic. 

They  may  be  divided  according  to  their  condition,  into — 
1.  Stratified ;  2.  Unstratified. 

Unstratified  rocks  are  either  igneous  or  metamorphic. 

Bocks  which  contain  organic  remains  are  said  to  be 
fossiliferous ;  if  destitute  of  these  remains,  non-fossil- 
iferous. 

Stratified  rocks  are  sometimes  called  fragmental.  Un- 
stratified rocks  are  sometimes  called  fragmental.  Aqueous 
rocks  are  sometimes  called  sedimentary. 

During  the  geological  past  extensive  changes  occurred  in 
the  land  and  water  surface  of  the  earth,  and  in  the  plants 
and  animals  inhabiting  it. 

The  changes  now  occurring  in  the  earth's  crust  are 
caused — 1.  By  the  winds;  2.  By  the  moisture  of  the 
atmosphere;  3.  By  the  action  of  running  water;  4.  By 
the  agency  of  man ;  5.  By  the  action  of  the  heated  in- 
terior. 

Of  the  197,000,000  square  miles  of  the  earth's  surface, 
144,000,000  square  miles  are  covered  by  water,  and 
53,000,000  by  land.     The    proportion  between  the  land 


and  water  is  very  nearly  as  the  square  of  three  is  to  the 
square  of  five. 

The  continents  extend  farther  to  the  north  than  to  the 
south ;  they  are  crowded  together  near  the  north  pole. 
Their  southern  projections  are  separated  from  each  other 
by  extensive  oceans. 

Nearly  all  the  land  masses  are  collected  in  one  hemi- 
sphere, and  a  large  part  of  the  water  in  another. 

There  are  two  great  systems  of  trends  or  lines  of  direc- 
tion, along  which  the  shores  of  the  continents,  the  moun- 
tain-ranges, the  oceanic  basins,  and  the  island  chains 
extend. 

The  main  prolongation  of  the  eastern  continent  is  in  the 
direction  of  the  north-eastern  trend ;  the  western,  in  that 
of  the  north-western  trend. 

The  coast  lines  of  the  northern  continents  are  very  irreg- 
ular, the  shores  being  deeply  indented  with  gulfs  and  bays, 
while  those  of  the  southern  continents  are  comparatively 
simple  and  unbroken. 

Of  the  53,000,000  square  miles  of  the  land,  3,000,000,  or 
about  one-seventeenth,  is  composed  of  islands. 

Islands  are  either  continental  or  oceanic. 

Continental  islands  are  detached  portions  of  the  neigh- 
boring continents. 

Oceanic  islands  are  the  summits  of  submarine  mountain- 
chains.  They  are  either  high  or  low :  the  high  oceanic 
islands  are  generally  of  volcanic  formation  ;  the  low  islands 
are  of  coral  formation.  Mangrove  islands  occur  off  the 
coasts  of  Florida. 

There  are  four  varieties  of  coral  formations :  1.  Fringing 
reefs;  2.  Barrier  reefs ;  3.  Encircling  reefs ;  4.  Atolls. 

A  peculiar  variety  of  coral  reef  occurs  off  the  coasts  of 
Florida. 

The  subsidence  of  the  ocean's  bed  is  proved — 1.  By  the 
exclusive  occurrence  of  volcanoes  on  the  shores  of  the  con- 
tinents or  on  islands;  2.  By  the  occurrence  of  atolls  or 
coral  islands;  3.  By  the  general  direction  of  the  continen- 
tal island  chains. 

The  earth's  surface  is  composed  of  high  lands  and  low 
lands.  The  dividing  line  is  1000  feet  above  the  level  of 
the  sea. 

High  lands  are  either  mountainous  or  plateaus. 

Low  lands  are  either  hills  or  plains. 

About  one-half  of  the  land  surface  of  the  earth  is  occu- 
pied by  plains. 

Plains  are  1.  Undulating ;  2.  Marine;  3.  Alluvial. 

Mountains  were  formed  by  the  contraction  of  the  earth's 
crust,  producing  a  lateral  pressure  on  extended,  thick  de- 
posits of  sedimentary  rocks.  Slaty  cleavage  was  caused 
by  this  lateral  pressure. 

The  following  peculiarities  are  noticeable  in  the  relief 
forms  of  the  continents : 

1.  The  continents  have,  in  general,  high  borders  and  a 
low  interior. 

2.  The  highest  border  lies  nearest  the  deepest  ocean ; 
hence,  the  culminating  point,  or  the  highest  point  of  land, 
lies  out  of  the  centre  of  the  continent. 

3.  The  greatest  prolongation  of  a  continent  is  always 
that  of  its  predominant  mountain-system. 

4.  The  prevailing  trends  of  the  mountain  masses  are  the 
same  as  those  of  the  coast  lines,  and  are,  in  general,  either 
north-east  or  north-west. 

Water  acquires  its  maximum  density  at  about  the  tem- 
perature of  39.2°  Fahr. 

Water  requires  more  heat  to  warm  it,  and  gives  out  more 
on  cooling,  than  any  other  common  substance. 

During  the  constant  washings  to  which  the  continents 


GENERAL    SYLLABUS. 


161 


are  subjected  by  the  rains,  their  surfaces  are  cleansed  of 
the  decaying  animal  and  vegetable  matters  which  cover 
them. 

The  drainage  of  the  laud  is  of  two  kinds :  subterranean 
and  surface,  drainage. 

Surface  drainage  is  either  oceanic  or  inland. 

According  to  the  size  of  their  reservoirs,  springs  are 
either  constant  or  temporary ;  according  to  the  depth  of  the 
reservoirs,  they  are  either  cold  or  hot ;  according  to  the 
nature  of  the  mineral  substances  lining  their  reservoirs, 
they  become  charged  with  various  mineral  substances ;  if 
their  reservoirs  discharge  through  a  siphon-shaped  tube, 
they  are  periodical ;  if  their  reservoirs  are  formed  of  con- 
cave layers,  they  are  called  artesian  springs. 

The  quantity  of  water  discharged  by  a  river  depends— 
1.  On  the  size  of  its  basin.  2.  On  the  amount  of  its  rain- 
fall. 3.  On  the  climate  of  its  basiu,  a  dry,  hot  air  dimin- 
ishing the  quantity  by  evaporation.  4.  On  the  nature  of 
its  bed  or  channel,  whether  leaky  or  not.  5.  On  the 
features  of  its  basin,  whether  wooded  or  open. 

The  material  eroded  by  a  river  is  deposited— 1.  In  the 
channel  of  the  river.  2.  On  the  alluvial  flats  or  flood- 
grounds.  3.  At  the  mouth.  4.  Along  the  coast  near  the 
mouth. 

In  the  upper  courses  of  rivers  erosion  occurs  mainly  on 
the  bottom  of  the  channel ;  in  the  lower  courses,  at  the 
sides. 

The  Atlantic  and  Arctic  Oceans  receive  the  waters  of 
nearly  all  the  large  river  systems  of  the  world. 

Lakes  connected  with  the  system  of  oceanic  drainage  are 
generally  fresh ;  those  connected  with  the  inland  drainage 
are  generally  salt. 

The  bed  of  the  ocean  is  less  diversified  than  the  surface 
of  the  land. 

The  greatest  depth  of  the  ocean  is  probably  greater  than 
the  greatest  elevation  of  the  land. 

The  articulation  of  land  and  water  assumes  four  dis- 
tinct forms, — inland  seas,  border  seas,  gulfs  aud  bays, 
and  fiords. 

Inland  seas  characterize  the  Atlantic ;  border  seas,  the 
Pacific ;  gulfs  and  bays,  the  Indian ;  fiords,  the  Atlantic 
aud  Pacific. 

A  deposit  of  fine  calcareous  mud  or  ooze,  formed  of  the 
hard  parts  of  minute  animalcule,  occurs  over  extended 
areas  of  the  floor  of  the  ocean. 

Tides  are  caused  by  the  attraction  of  the  sun  and  moon  ; 
spring  tides  by  their  combined  attractions ;  neap  tides,  by 
their  opposite  attractions. 

Constant  ocean  currents  are  occasioned  by  the  heat  of  the 
sun  and  the  rotation  of  the  earth. 

The  vertical  rays  of  the  sun  are  warmer  than  the  oblique 
rays — 1.  Because  they  have  a  less  depth  of  air  to  pass 
through.  2.  Because  they  are  spread  over  a  smaller  area. 
3.  Because,  striking  the  surface  more  directly,  they  produce 
greater  heat. 

Continual  summer  characterizes  the  tropics ;  summer  and 
winter  of  nearly  equal  duration,  the  temperate  zones  ;  and 
short,  hot  summers,  followed  by  long,  intensely  cold  win- 
ters, the  frigid  zones. 

The  irregular  distribution  of  heat  over  the  earth  is 
caused — 1.  By  the  irregularities  of  the  surface.  2.  By  pecu- 
liarities in  the  distribution  of  the  land-  and  water-areas. 
3.  By  the  influence  of  the  winds  and  ocean  currents.  4. 
By  the  nature  of  the  surface. 

Winds  are  caused  by  the  disturbance  of  the  equilibrium 
of  the  atmosphere  by  heat. 

The  general  motion  of  the  surface  winds  is  towards  an 


area  of  greatest  heat;  of  the  upper  currents,  towards  an 
area  of  least  heat. 

The  general  atmospheric  circulation  is  from  the  equator 
to  the  poles,  and  from  the  poles  to  the  equator. 

In  storms,  the  wind  has  a  rotary  motion  around  an  area 
of  low  barometer,  which,  at  the  same  time,  progresses  along 
the  surface. 

In  the  northern  hemisphere,  the  rotary  motion  is  in  an 
opposite  direction  to  the  hands  of  a  clock ;  in  the  southern 
hemisphere,  in  the  same  direction  as  the  hands  of  a  clock. 

Moisture  may  be  precipitated  from  the  air  in  the  form  of 
dew,  mist,  fog,  cloud,  rain,  hail,  sleet,  or  snow. 

In  order  that  any  form  of  precipitation  may  occur,  the 
air  must  be  reduced  below  the  temperature  of  its  dew- 
point. 

Glaciers  are  immense  masses  of  ice  and  snow,  which 
move  with  extreme  slowness  down  the  higher  valleys  of 
mountain-ranges.  They  resemble  rivers  in  that  they  re- 
ceive through  the  drainage  of  their  basins,  the  solid 
material  which  flows  into  them. 

The  snow  line  is  the  distance  above  the  sea  where  the 
snow  remains  throughout  the  year.  The  height  of  its 
lower  level  above  the  sea  depends  (1.)  On  the  amount  of 
the  snowfall.  (2.)  On  the  temperature  of  the  valley.  (3.) 
On  the  inclination  of  the  slope. 

The  unit  of  electric  potential  is  called  a  volt;  the  unit 
of  current  an  ampere;  the  unit  of  resistance  an  ohm. 
Comparing  the  flow  of  electricity  to  a  current  of  water  in 
a  pipe,  the  volt  corresponds  to  the  pressure  causing  the 
flow,  the  ohm  to  the  resistance,  or  friction,  opposing  it, 
and  the  ampere  to  the  quantity  of  flow  per  second. 

The  principal  electrical  phenomena  of  the  atmosphere  are 
thunder  and  lightning,  St.  Elmo's  fire,  and  the  aurora. 

The  principal  optical  phenomena  are  the  rainbow,  the 
mirage,  halos,  and  coronse. 

The  earth  acts  like  a  huge  magnet.  Its  magnetism  is 
probably  due  to  the  circulation  around  it  of  electrical  cur- 
rents, generated  by  the  sun's  heat. 

The  true  basis  for  the  distribution  of  vegetation  is  the 
distribution  of  the  light,  heat,  and  moisture,  upon  which 
its  existence  mainly  depends. 

The  variety  and  luxuriance  of  vegetation  decrease  as 
we  pass  from  the  equator  to  the  poles,  or  from  the  base 
of  a  mountain  to  the  summit. 

The  principal  food-plants  of  the  tropical  regions  are  rice, 
bananas,  plantains,  dates,  cocoa-nuts,  cassava,  bread-fruit, 
sago,  and  yams. 

Coffee,  tea,  cocoa,  pepper,  cloves,  nutmegs,  and  vanilla 
are  also  products  of  the  tropics. 

The  principal  food-plants  of  the  temperate  zones  are 
barley,  rye,  wheat,  oats,  maize  or  Indian  corn,  buckwheat, 
and  the  potato. 

Animals  are  restricted,  by  conditions  of  food  and  climate, 
to  certain  regions  of  the  earth. 

They  are  dependent  for  their  continued  existence  upon 
plants,  the  distribution  of  which  therefore  forms  an  excel 
lent  basis  for  the  distribution  of  animals. 

With  a  few  exceptions,  animals  possess  but  little  power 
of  becoming  acclimated,  or  living  in  a  climate  differing 
greatly  from  that  in  which  they  were  created. 

The  grassy  meadows  and  prairies  in  North  America  cause 
the  fauna  of  the  continent  to  be  characterized  by  a  pre- 
ponderance of  plant-eating  mammals.  Its  extensive  lake- 
and  river-systems  harbor  a  great  number  and  variety  of 
waterfowl. 

South  America  is  characterized  by  the  predominance  of 
its  reptiles  and  insects.     Birds  are  also  numerous. 


162 


PHYSICAL    GEOGRAPHY. 


Asia  is  the  home  of  domesticated  animals. 

Australia  is  the  home  of  the  marsupials. 

The  luxuriant  vegetation  of  the  south  of  Africa  sustains 
some  of  the  largest  of  the  mammalia,  such  as  the  elephant, 
rhinoceros,  hippopotamus,  and  giraffe. 

The  entire  human  family  has  descended  from  a  single 
pair  or  species. 

The  primary  races  of  rueii  are  the  Caucasian,  the  Mongo- 
lian, and  the  Negro. 

The  secondary  races  are  the  Malay,  the  American,  and 
the  Australian. 

The  coast  line  of  the  United  States  is  comparatively 
simple  and  unbroken. 

The  predominant  mountains  are  in  the  west ;  the  second- 
ary mountains  are  in  the  east. 

The  great  low  plains  of  the  United  States  are  the  Atlantic 
coast  plain  and  the  plain  of  the  Mississippi  Valley. 

The  United  States  lies  in  the  physical  north  temperate 
and  the  physical  torrid  zone. 


The  climate  of  the  northern  half  of  the  Atlantic  coast 
is  much  colder  than  that  of  the  northern  half  of  the 
Pacific. 

The  United  States  lies  in  the  zone  of  the  variable 
winds. 

The  heaviest  rainfall  is  on  the  Pacific  coast  and  near  the 
borders  of  the  Gulf  States. 

There  are  four  distinct  plant  regions:  the  forest,  the 
prairie,  the  steppe,  and  the  Pacific. 

The  Territory  of  Alaska  occupies  an  area  of  550,000 
square  miles. 

The  Territory  of  Alaska  is  mainly  mountainous.  The 
shore  lands  of  the  Arctic  are  frozen  moor-lands  like  the 
tundra?  of  Asia. 

The  Yukon  and  Kuskovim  are  the  principal  rivers. 

Myriads  of  salmon  visit  the  rivers  during  the  breeding 
season. 

Valuable  food-fish  are  found  in  the  waters  off  the  coasts. 

Numerous  fur-bearing  animals  are  found  in  Alaska. 


GENERAL  REVIEW   QUESTIONS. 


Mathematical  Geography. 

What  is  the  earth's  position  in  the  solar  system  ? 

How  much  larger  is  the  sun  than  the  earth? 

Of  what  use  are  latitude  and  longitude  ? 

Distinguish  between  a  map  of  the  earth  on  a  Mercator's 
projection,  and  maps  on  equatorial  aud  polar  and  conical 
projections. 

Explain  the  cause  of  the  change  of  day  and  night. 

Explain  the  causes  of  the  change  of  seasons. 

The  Land. 

Enumerate  the  proofs  of  the  present  heated  condition 
of  the  interior  of  the  earth. 

What  is  the  theory  for  the  exclusive  occurrence  of  vol- 
canoes near  the  borders  of  the  ocean  ? 

Why  is  it  unnecessary  to  consider  the  interior  of  the 
earth  as  in  a  fluid  condition  like  that  of  the  lava  ejected 
from  volcanoes  ? 

Name  the  principal  regions  of  active  volcanoes. 

What  facts  have  been  discovered  respecting  earthquake 
shocks  ?  Why  should  the  shocks  occur  more  frequently  at 
night  than  during  the  day,  or  during  winter  than  summer  ? 

Into  what  two  classes  may  unstratified  rocks  be  divided  ? 

Explain  the  origin  of  coal. 

Enumerate  some  of  the  changes  which  are  now  taking 
place  in  the  crust  of  the  earth. 

What  are  the  relative  land-  and  water-areas  of  the  earth  ? 

Describe  the  land  hemisphere.    The  water  hemisphere. 

What  do  you  understand  by  lines  of  trend? 

Which  of  the  continents  contains,  in  proportion  to  its 
area,  the  greatest  length  of  coast  line  ?    Which  the  least  ? 

Distinguish  between  continental  and  oceanic  islands; 
between  coral  and  volcanic  islands. 

Why  does  the  presence  of  an  atoll  in  any  part  of  the 
ocean  prove  the  subsidence  of  its  bed  at  that  point?  Ex- 
plain the  nature  of  the  coral  formations  off  the  southern 
coast  6f  Florida. 

What  do  you  understand  by  the  forms  of  relief  of  the 
land? 

Distinguish  between  a  mountain  and  a  hill.  A  plateau 
and  a  plain. 


What  peculiarities  are  noticeable  in  the  general  relief 
forms  of  the  continents? 

Which  of  the  continents  resemble  each  other  in  the  gen- 
eral arrangement  of  their  relief  forms  ?  In  what  respect 
do  they  all  resemble  one  another  ? 

The  Water. 

Enumerate  the  principal  uses  of  water  in  the  economy 
of  the  earth. 

What  effect  has  the  high  specific  heat  of  water  on  the 
climate  of  maritime  countries? 

What  is  the  cause  of  the  heat  developed  during  the  con- 
densation of  a  mass  of  vapor  ? 

Distinguish  between  subterranean  and  surface  drainage. 

Explain  in  general  the  origin  of  springs. 

Into  what  different  classes  may  springs  be  divided  ac- 
cording to  the  size  of  their  reservoirs?  According  to 
the  shape?  The  location?  The  shape  of  the  outlet 
tube? 

Define  calcareous,  silicious,  sulphurous,  chalybeate,  brine, 
and  acidulous  springs. 

Define  river-system,  basin,  water-shed,  source,  channel, 
and  mouth. 

Explain  the  origin  of  waterfalls. 

By  what  are  the  inundations  of  rivers  caused? 

What  is  silt?  In  what  different  parts  of  a  river-system 
may  silt  be  deposited  ?    Define  fluvio-marine  formations. 

In  what  respects  do  the  drainage-systems  of  North  and 
South  America  resemble  each  other? 

In  what  respects  do  the  river-systems  of  Africa  resemble 
those  of  the  Americas? 

Why  are  the  waters  of  lakes  with  no  outlets  generally 
salt? 

Name  the  great  fresh-water  lake-systems  of  the  world. 

State  the  composition  of  ocean-water.  What  is  its 
density?    Its  boiling-point?    Its  color? 

How  do  the  five  oceans  compare  with  one  another  in 
area? 

Distinguish  between  inland  seas,  border  seas,  and  gulfs 
and  bays,  and  fiords. 

What  facts  are  known  respecting  the  shape  of  the  bed  of 


GENERAL    REVIEW   AND    MAP    QUESTIONS 


163 


the  Atlantic  Ocean  ?  Of  the  Indian  Ocean  ?  Explain  the 
origin  of  the  ooze-deposits  on  the  ocean's  beds. 

By  what  are  waves  caused?  Upon  what  does  their 
height  depend? 

How  are  tides  caused  ? 

Distinguish  between  ebb,  flood,  spring,  and  neap  tides. 

Where  does  the  parent  tidal  wave  originate? 

In  what  part  of  the  ocean  are  tides  the  highest? 
Why? 

What  are  the  main  causes  of  constant  oceanic  currents? 

In  what  respects  do  the  currents  in  the  three  central 
oceans  resemble  one  another? 

The  Atmosphere. 

What  is  the  composition  of  the  atmosphere  ? 

By  what  instrument  is  the  pressure  of  the  atmosphere 
measured? 

What  proof  have  we  that  the  greater  weight  of  the  at- 
mosphere lies  within  a  few  miles  of  the  earth's  surface? 

Define  climate.  Enumerate  the  circumstances  which 
influence  the  climate  of  a  country. 

Why  are  the  vertical  rays  of  the  sun  warmer  than  the 
oblique  rays? 

In  what  different  ways  does  the  atmosphere  receive  its 
heat  from  the  sun  ? 

Explain  the  origin  of  winds. 

Why  should  the  general  direction  of  the  atmospheric 
circulation  be  between  the  equator  and  the  poles? 

Name  the  different  wind  zones  of  the  earth. 

What  is  the  origin  of  laud  and  sea  breezes? 

What  resemblance  do  land  and  sea  breezes  bear  to 
monsoons  ? 

Describe  some  of  the  peculiarities  of  cyclones. 

What  facts  have  been  discovered  in  regard  to  the  great 
storms  of  the  United  States  ? 

Enumerate  the  circumstances  upon  which  the  rapidity 
of  evaporation  depends. 

State  the  general  law  for  the  occurrence  of  precipi- 
tations. 

Under  what  circumstances  will  a  heavy  deposition  of 
dew  occur? 

Name  the  primary  forms  of  clouds.  The  secondary 
forms. 

Explain  the  peculiarities  of  the  rainfall  in  each  of  the 
wind  zones. 

Why  is  the  rainfall  on  mountains  heavier  than  that  on 
plains? 

Define  snow  line.  On  what  three  circumstances  does  the 
height  of  the  snow  line  depend  ? 

Describe  the  formation  of  a  glacier. 

Enumerate  the  principal  electrical  and  optical  phenom- 
ena of  the  atmosphere. 


What  is  the  probable  cause  of  the  earth's  magnetism  ? 
Define  volt,  ohm,  ampere.  What  analogies  exist  between 
the  flow  of  water  in  a  pipe  and  an  electric  current  ? 

Organic    Life. 

Why  should  the  distribution  of  light,  heat,  and  moisture 
form  the  best  basis  for  the  distribution  of  vegetation  ? 

Define  flora.  Distinguish  between  the  horizontal  and 
the  vertical  distribution  of  vegetation. 

State  the  limits  of  each  of  the  horizontal  zones  of 
vegetation. 

What  is  the  characteristic  feature  of  the  flora  of  each  of 
these  zones? 

State  the  conditions  requisite  for  the  existence  of  forests ; 
of  prairies ;  of  steppes ;  of  deserts. 

Enumerate  the  principal  cultivated  plants  of  the  torrid, 
temperate,  and  polar  zones. 

Define  fauna. 

Upon  what  is  the  existence  of  animal  life  dependent? 

What  is  the  cause  of  the  change  noticed  in  the  fauna  in 
passing  from  the  equatbr  to  the  poles,  or  from  the  base  to 
the  summit  of  a  high  tropical  mountain? 

Enumerate  the  characteristic  tropical  fauna ;  the  temper- 
ate fauna ;  the  arctic  fauna. 

What  is  the  characteristic  peculiarity  of  the  fauna  of 
each  of  the  continents? 

Enumerate  the  proofs  of  the  probable  unity  of  the 
human  race. 

Name  the  portions  of  the  world  inhabited  by  each  of  the 
primary  and  secondary  races. 

Physical  Features  of  the  United  States. 

What  is  the  area  of  the  United  States,  exclusive  of 
Alaska  ? 

Describe  the  surface  structure  of  the  United  States. 

Describe  the  drainage-systems  of  the  United  States. 

What  are  the  causes  of  the  difference  in  the  temperature 
of  the  eastern  and  western  coasts? 

Between  what  extremes  of  mean  annual  temperature  are 
the  United  States  included? 

In  what  wind  zone  is  the  United  States  situated? 

Name  the  four  principal  regions  of  vegetation. 

Enumerate  the  chief  agricultural  productions  of  the 
country. 

What  large  animals  are  found  in  the  United  States? 

Name  the  chief  mineral  productions. 

What  is  the  area  of  Alaska  ? 

What  are  the  principal  indentations  of  its  coast? 

Name  the  principal  islands  of  Alaska. 

Describe  the  river-system  of  the  Yukon. 

Name  the  principal  trees  of  Alaska.  Name  its  principal 
fur-bearing  animals.    Its  principal  food-fishes. 


GENERAL    MAP    QUESTIONS. 


°i*ic 


Volcanoes  and  Earthquakes. 

Describe  the  volcanic  districts  of  the  Pacific  Ocean. 

In  what  portions  of  these  districts  are  volcanoes  most 
numerous  ? 

Describe  the  volcanic  districts  of  the  Indian  Ocean. 

In  what  direction  do  most  of  the  lines  of  fracture  in 
this  ocean  extend? 


Describe  the  volcanic  districts  of  the  Atlantic. 

Where  are  submarine  eruptions  most  numerous  in  this 
ocean  ? 

Describe  the  earthquake  dfstrict  of  the  Mediterranean 
Sea  and  Central  Asia. 

What  other  portions  of  the  world  are  especially  liable  to 
earthquake  shocks? 


164 


PHYSICAL    GEOGRAPHY. 


Name  the  parts  of  the  world  shaken  by  the  great  earth- 
quake of  Lisbon,  in  1755. 

Oceanic  Areas  and  River-Systems. 

What  two  oceans  receive  the  drainage  of  the  greatest 
areas  of  the  continents'' 

State,  from  a  careful  inspection  of  the  direction  in  which 
the  principal  river-systems  flow,  the  direction  of  inclina- 
tion of  the  principal  slopes  of  the  continents. 

Observe  that  in  most  of  the  continents  there  is  a  long 
gentle  slope  and  a  short  abrupt  slope;  state  the  general 
direction  of  each  of  these  slopes. 

Locate  the  principal  systems  of  inland  drainage  in  each 
of  the  continents. 

Name  the  principal  lakes  and  rivers  belonging  to  the 
larger  of  these  systems. 

Describe  in  general  the  river-systems  of  the  Atlantic,  or 
the  rivers  draining  into  the  Atlantic.  Describe  the  river- 
systems  of  the  Pacific.    Of  the  Indian.    Of  the  Arctic. 

Enumerate  the  five  largest  rivers  belonging  to  each  of 
these  river-systems. 

Name  the  principal  rivers  of  the  world  which  have  delta 
mouths. 

What  are  the  land  and  water  boundaries  of  each  of  the 
five  oceans  ? 

Ocean  Currents. 

What  is  the  general  direction  of  the  equatorial  ocean 
currents?  Explain  the  cause  of  this  general  direction. 
What  exception  can  you  find  to  it  ? 

What  is  the  general  direction  of  the  Arctic  currents  ?  Of 
the  Antarctic  currents  ? 

What  are  the  causes  of  these  general  directions  ? 

Describe  the  principal  currents  of  the  Atlantic ;  of  the 
Pacific;  of  the  Indian  Ocean. 

Locate  the  principal  grassy  seas. 

Explain  the  cause  of  these  seas. 

Name  the  principal  warm  ocean  currents ;  the  principal 
cold  ocean  currents. 

Name  some  cold  currents  which  powerfully  affect  the 
climate  of  different  parts  of  the  earth  ?  Name  some  warm 
currents  which  powerfully  affect  the  climate. 

In  what  respects  do  the  general  directions  of  the  cur- 
rents in  each  of  the  central  oceans  resemble  one  another  ? 

Name  the  points  of  resemblance  between  the  Gulf 
Stream  and  the  Japan  Current. 

Isothermal  Lines  and  Physical  Zones. 

Point  out  the  most  striking  deviations  in  the  directions 
of  the  isothermal  lines  from  the  parallels  of  latitude. 

Explain  in  each  case  the  main  cause  of  these  deviations. 

In  what  part  of  the  world  do  the  isothermal  lines  coin- 
cide most  nearly  with  the  parallels  ? 

Trace  on  the  map  the  isothermal  line  of  79°  Fahr.  Of 
32°  Fahr.     Of  40°  Fahr. 

In  what  parts  of  the  world  is  the  highest  temperature 
found  during  the  month  of  July  ? 

What  is  the  temperature  of  the  greatest  cold  of  Jannary  ? 
Where  is  it  found? 

What  is  the  mean  temperature  of  London  for  January  ? 
For  July  ?  What  other  large  cities  have  nearly  the  same 
mean  July  or  January  temperature  as  London  ? 

What  is  the  mean  temperature  of  Bombay  for  January? 
For  July?  What  other  large  cities  have  nearly  the  same 
mean  July  or  January  temperature  as  Bombay? 


Point  out  the  northern  limit  of  drift  ice.  The  southern 
limit. 

Why  is  it  advantageous  for  a  vessel  sailing  from  England 
or  America  via,  the  Cape  of  Good  Hope  to  maintain  an 
easterly  direction  both  going  and  returning? 

Describe  the  boundaries  of  the  physical  torrid,  tem- 
perate, and  frigid  zones. 

Name  the  principal  countries  which  lie  wholly  or  in  part 
in  each  of  these  zones. 

Winds,  Rain,  and  Ocean-Routes. 

State  the  boundaries  of  each  of  the  wind  zones. 

What  is  the  general  direction  of  the  wind  in  each  of 
these  zones? 

Name  the  principal  monsoon  regions  of  the  world. 

Enumerate  the  principal  mountain  and  desert  winds. 

What  is  the  direction  of  the  rotation  of  the  wind  in  the 
cyclonic  storms  of  the  northern  hemisphere  ?  Of  the  south- 
ern hemisphere  ? 

Name  the  principal  storm-regions  of  the  world. 

Describe  the  characteristic  rainfall  in  each  of  the  princi- 
pal wind  zones. 

What  would  be  the  general  route  of  a  vessel  in  sailing 
from  America  to  Europe,  and  back  again  ?  From  Europe 
to  San  Francisco? 

What  two  sailing  routes  are  there  from  Europe  to  Aus- 
tralia or  India  ? 

Vegetation. 

Give  the  boundaries  of  each  of  the  plant  zones. 

State  the  countries  or  portions  of  countries  which  lie  in 
each  of  these  zones. 

Name  some  of  the  useful  plants  of  each  of  these  zones. 

Point  out  on  the  map  the  northern  limit  of  trees.  The 
southern  limit. 

Name  the  portions  of  the  world  from  which  valuable 
timber  is  obtained. 

What  are  the  principal  tea-  and  coffee-growing  countries 
of  the  world  ? 

Where  are  the  principal  forests  ? 

Animals. 

What  limits  are  assumed  as  the  boundaries  of  the  tropi- 
cal, temperate,  and  arctic  fauna? 

Name  the  principal  tropical,  temperate,  and  arctic 
fauna  ? 

What  domesticated  animals  are  found  in  the  tropical  and 
temperate  zones? 

Trace  on  the  map  the  northern  limit  of  the  camel  and 
of  the  reindeer  ;  of  monkeys.  The  southern  limit  of  the 
camel ;  of  monkeys ;  of  the  polar  bear,  and  of  the  elephant 
and  rhinoceros. 

In  what  parts  of  the  world  are  the  whale,  seal,  and  wal- 
rus found  ? 

Describe  the  limits  of  the  grizzly  bear.    Of  the  musk-ox. 

What  are  the  characteristic  animals  of  the  New  World  ? 
Of  the  Old  World? 

State  the  characteristic  fauna  of  North  America.  Of 
South  America.    Of  Europe,  Asia,  Africa,  and  Australia. 

The  Races  of  Men. 

Trace  on  the  map  the  northern  and  southern  limits  of 
permanent  habitation. 

Name  all  the  countries  of  the  world  inhabited  by  the 
Caucasian  race. 


GENERAL    MAP    QUESTIONS, 


165 


In  what  parts  of  the  world  are  the  Caucasians  mixed  with 
other  races  ? 

Name  the  different  countries  of  the  world  inhabited  by 
the  Mongolian  race. 

Name  some  of  the  different  peoples  belonging  to  this 
race. 

What  parts  of  the  world  are  peopled  by  the  Ethiopian, 
or  Negro  race  ? 

Name  some  of  the  different  tribes  belonging  to  this  race. 

Name  the  different  countries  of  the  world  inhabited  by 
the  secondary  races  of  men  ? 

Give  the  names  of  the  principal  tribes  of  each  of  the 
secondary  races. 

What  different  races  of  men  inhabit  North  America? 
South  America?    Europe?    Asia?    Africa?    Australia? 
19 


Physical  Map  of  the  United  States. 

Describe  from  the  map  the  forms  of  relief  of  the  United 
States. 

Name  the  principal  mountain-ranges  belonging  to  the 
predominant  and  secondary  mountain-systems. 

Describe  the  drainage-systems  of  the  United  States. 

What  large  lake-system  is  situated  in  the  north-eastern 
part  of  the  United  States  ? 

Trace  on  the  map  the  general  directions  of  the  principal 
isothermal  lines,  showing  the  hottest  and  coldest  portions 
of  the  country. 

Name  the  principal  islands  which  lie  near  the  coasts  of 
the  United  States. 

Name  the  fluvio-marine  formations  of  the  eastern 
coast. 


Pronouncing  Vocabulary. 


=-*«= 


SOUNDS   OF  THE  LETTERS. 


Vowels. 
Fate,  fir,  fall,  fit,  a  (obscure),  as  in  organ,  oval ;  ah,  inter- 
mediate between  a  and  a,  as  in  al-a-bah'-ma ;  aa  or  a  long ; 
me,  m§t,  e,  as  in  berth,  ravel ;  pine  or  pine,  pin,  i,  as  in  firm, 
evil ;  no,  not,  9,  as  in  sermon,  harbor ;  00,  as  in  moon ;  55,  as 
in  good;  ow,  as  in  now;  ii,  as  in  tube;  fl,  as  in  tub;  ii,  the 
French  eu,  nearly  like  u  in  tub,  or  fur ;  y  and  ey,  at  end  of 
unaccented  syllable,  like  e  in  me;  ai  and  ay,  like  a  in  fate; 
au  and  aw,  as  a  in  fall ;  eS,  as  i  in  pit ;  5w  or  au,  as  now  or  our. 

Consonants. 
Th  as  in  thin ;  th,  as  in  this ;  d,  as  th,  in  this ;    G  and 
K,  sound  of  the  German  ch,  somewhat  like  our  h,  strongly 


aspirated.  3  indicates  a  blending  of  the  sounds  of  n  and  y ; 
I,  a  blending  of  1  and  y ;  m  and  n  and  n°,  nasal,  like  our  ng  ; 
R,  like  rr  in  terror ;  w,  like  our  v.  Pronounce  all  other  letters 
as  in  English. 

The  primary  or  principal  accent  is  marked  thus  (');  the 
secondary,  thus  (*). 

In  determining  the  correct  pronunciation  of  a  word,  first 
sound  the  separate  syllables  distinctly,  repeating  the  process 
several  times ;  afterward  pronounce  the  whole  word  smoothly 
and  continuously,  being  careful  to  mark  the  accents;  e.g. 
Nevada,  ni-va'-da,  nay-vah'-dah ;  Apache,  l-pa'-cha,  ah- 
pah'-chay;    Canada,  kan'-a-da,  kan'-uh-duh. 


A. 

Abyssinia,  ab-is-sin'-e-a. 

Aconcagua,  a-kon-ka'-gwa. 

Adelsberg,  a'-dels-berg\ 

Adriatic,  adv-re-at'-ic. 

Afghanistan,  af-ganv-is-tan'. 

Agulhas,  a-gool'-yas. 

Alabama,  al-a-bah'-ma. 

Alaska,  al-as'-ka. 

Albemarle,  al-be-marl'. 

Aleutian,  a-lu'-she-an. 

Algiers,  al-jeerz'. 

Alleghanies,  al-le-ga'-nees. 

Altamaha,  al-ta-ma-haw'. 

Amazon,  am'-a-zon. 

Amboyna,  am-boi'-nl. 

Amoo,  a-moo'. 

Amoor,  a-moor'. 

Anahuac,  an-a-wack'. 

Anatolia,  an-a-to'-le-a. 

Antioosti,  an-te-kos'-tee. 

Antilles,  anMeel'. 

Antisana,  In-te-sa'-na. 

Appalachicola,  ap^-pa-lah^-che-ko'-la. 

Apennines,  ap'-en-ninzv. 

Appalachian,  ap-pa-la'-che-an. 

Apsheron,  ap-sha-ron'. 

Ararat,  ar'-a-rat\ 


Archangel,  ark-an'-jel. 
Arequipa,  a-ra-kee'-pa. 
Arizona,  arv-i-zo'-na. 
Arkansas,  ar-kan'-sas. 
Armenia,  ar-mee'-ne-a. 
Arveiron,  aiO-vI-ron\ 
Asia,  a'-she-a,  not  a'-zhe-a. 
Atacama,  a-ta-ka'-ma. 
Athabasca,  ath'-a-bas'-ka. 
Auckland,  awk'-land. 
Auvergne,  ov-vairfl'. 
Azores,  az'-ors,  or  az-orz'. 
Azov,  az'-ovv,  or  1-zov'. 


B. 

Babylonian,  bab-e-lo'-ne-an. 

Bahamas,  ba-ha'-ma. 

Baikal,  bi'-kal. 

Baku,  bav-koo\ 

Balkan,  bal-kan'. 

Balkash,  bar-kash'. 

Baltimore,  bawl'-te-moce,  or  bawlt'-e- 

mpr. 
Banda,  ban'-da. 
Barbadoes,  bar-ba'-dpz. 


Batavia,  ba-ta'-ve-a. 

Baton  Bonge,  bat'-9n-roozh. 

Bedouins,  bed'-oo-inz. 

Beled-el-Jerid,  bel'-ed-el-jer-eed'. 

Beloochistan,  bel-oov-chis-tan'. 

Belor,  or  Bolor,  b6-lor'. 

Bengal,  ben-gawl\ 

Berlin,  ber'-lin. 

Bermudas,  ber-moo'-daz. 

Ber&ina,  ber-nee'-ni. 

Bohemian,  bo-hee'-me-an. 

Bolivia,   bo-liv'-e-a.      (Spanish  pron., 

bo-lee'-ve-a.) 
Bombay,  bom-ba'. 
Boothia  Felix,  boo'-the-a  fe'-liks. 
Bourbon,  bfir'-b9n. 
Brahmapootra,  brahv-ma-poo'-tra. 
BrazOS,  brah'-zos. 
Buenos  Ayres,  bo'-n9s  a'-riz,  or  bo'- 

nos  airz.     (Spanish  pron.,  bwa'-noce 

I'-rSs.) 


c. 

Cairo,  ki'-ro. 
Calabria,  ka-la'-bre-q,. 
Calcutta,  kal-kut'-ta. 
Cambodia,  kam-b6'-de-a. 


166 


fate,  far,  fall,  fat,  me,  met,  pine,  pin,  no,  not,  organ,  b§rth,  firm,  serm9n,  tube,  tub,  thin,  thIs. 


PRONOUNCING   VOCABULARY.                                    167 

Cambridge,  kame-brij'. 

F. 

J. 

Cameroons,  cam-er-oons'. 

Cantabrian,  kan-ta'-bre-an. 

Falkland,  frwk'-land. 

Jamaica,  ja-ma'-ka. 

Canton,  kan-ton'. 

Fayal,  fill'. 

Jan  Mayen,  yan-mi'-en. 

Cape  Verde,  verd'. 

Feejee,  fee'-jee. 

Japan,  ja-pan'. 

Caribbean,  karv-rib-bee'-an. 

Fezzan,  feV-zan'. 

Java,  ja'-va,  or  jah'-va. 

Carpathian,  kar-pa'-the-an. 

Finsteraarhorn,  fins'-ter-aar-horn. 

Jorullo,  bo-rool'-yo,  or  ho-roo'-yo. 

Castile,  kas-teel'. 

Flores,  flo'-r£s. 

Cauca,  kow'-ka. 

Formosa,  for-mo'-sa. 

Caucasus,  kaw'-ka-sus. 

Fusi  Tama,  fu-si-ya-ma'. 

K. 

Cayenne,  ka-y3nn',  or  kr-Snn'. 

Celebes,  seT-e-bes. 

Kaffa,  kaf'-fa. 

Ceram,  se-rani'. 

G. 

Kalahari,  kal-a-ha'-re. 

Cevennes,  sa'-venn'. 

Kamtchatka,  kam-chat'-ka. 

Ceylon,  see'-lon,  or  sil-on'. 

Gairdner,  gard'-ner. 

Karakorum,  kav-ra-ko'-rum. 

Chagos,  cha'-g6s. 

Gallapagos,  ga-la'-pa-goce. 

Kenia,  ke'-ni-a. 

Chamouni,   shav-moo-nee'  (or  Chamo- 

Ganges,  gan'-gez. 

Kentucky,  ken-tuk'-ee. 

nix,  shax-mo-nee'). 

Gardafui,  gar'-da-fwee'. 

Kerguelen,  kerg'-e-len. 

Champlain,  sham-plane'. 

Garonne,  gav-ronn\ 

Keweenaw,  ke-wee'-naw. 

Charleston,  charlz'-ton. 

Gaudaloupe,  gwa-da-loo'-pa. 

Kilauea,  kev-16'-a-a. 

Chelyuskin,  chel-yus'-kin. 

Ghauts,  gawts. 

Kilimandjaro,  kir-e-manvja-ro\ 

Chicago,  she-kaw'-go. 

Gila,  heel'-a. 

Kinghan,  kin-gan'. 

Chili,  chil'-lee. 

Gilolo,  je-lo'-lo. 

Kiolen,  ky-6'-len,  or  cho'-len. 

Colima,  ko-lee'-ma. 

Greenwich,  grin'-idge. 

Kodiak,  ko'-de-ak. 

Colorado,  kol-o-rah'-do. 

Grenada,  gren-a'-da. 

Kong,  k6ng. 

Como,  ko'-mo. 

Grenelle,  greh'-nfill'. 

Kosciusko,  kos-se-us'-ko. 

Comorin,  com'-o-rin. 

Guadeloupe,  gawv-da-loop',  or  ga-deh- 

Kuen-lun,  kwSnMoon'. 

Comoro,  kom'-o-ro. 

loop'. 

Kunchinj unga,  koon -chin-j ung'-gl. 

Congo,  kong'-go. 

Guadiana,  gwa-de-a'-na. 

Kuvile,  koo'-ril. 

Constance,  kon-stants'. 

Guardafui,  gwar-da-fwee'. 

Cosiguina,  ko-se-ghee'-na. 

Guiana,  ghe-a'-ni. 

Guinea,  ghin'-nee. 

L. 

Laocadive,  lak'-ka-dlv\ 

D. 

H. 

Ladoga,  la'-do-ga. 

Ladrones,  lad-r6nz\ 

Dakota,  da-ko'-ta. 

Halle,  bal'-leta. 

Lapland,  lap'-land. 

Danube,  dan'-Qbe. 

Hartz,  haRts. 

La  Puebla,  11  pweV-ll. 

Deocan,  dfik'-kan. 

Havana,  ha-van'-a. 

Lauterbrunnen,  16w'-ter-brS5nx-nen. 

Demavend,  deW-a-vSnd'. 

Hawaii,  ha-wi'-ee. 

Lima,  lee'-ma. 

Detroit,  de-troit'. 

Hayti,  ba'-tee. 

Limpopo,  lim-po'-p6. 

Dhawalaghire,  da-w&T-a-gheV-ree. 

Hecla,  hek'-li. 

Llanos,  l'ya'-n&s. 

Dinario,  de-nar'-ic. 

Himalaya,  him-a-la'-ya,  or  him-a'-la- 

Llullayacu,  l'yoo-ryi-l'ya'-k6. 

Dnieper,  nee'-pr. 

y§» 

Loffoden,  lof-fo'-den. 

Dniester,  nees'-tgr. 

Hindoo-Koosh,  hin'-d5d'-koosh. 

Loire,  lwar. 

Dra,  dra. 

Hindostan,  hinMo-stan'. 

Lombardy,  lom'-bar-de. 

Duna,  dii'-na. 

Hoang-Ho,  ho-angv-ho',  nearly  wbangx- 

Loo  Choo,  loo^-chew'. 

Dwina,  dwi'-na,  or  hwee'-ni. 

ho'. 

Louisiana,  loo-ee-ze-ah'-na. 

Hoogly,  hoog'-lee. 

Louisville,  loo'-is-vil,  or  loo'-e-vil. 

Humber,  hum'-ber. 

Lowell,  lo'-el. 

Hungarian,  hung-ga'-re-an. 

Lupata,  lu-pa'-ta. 

E. 

Ecuador,  8k-wa-dor'. 

I. 

M. 

Edgecumbe,  ej'-kum. 

Edinburgh,  Sd'-in-bur-ruh. 

Iberian,  i-bee'-re-an. 

Hacao,  ma-k5w',  or  ma-ka-o. 

Elbe,  51b.     (Ger.  pron.,  eT-beh.) 

Ilaman,  or  Illimani,  eer-ya-ma'-ne. 

Mackenzie,  mak-ken'-zee. 

Elbruz,  eT-brooz'. 

Illinois,  ir-lin-oi'. 

Madagascar,  mad^-a-gas'-kar. 

Elton,  eT-ton'. 

Indiana,  inv-de-an'-a,  or  in-de-ah'-na. 

Madeira,  ma-dee'-ra,  or  ma-da' -ra. 

Euphrates,  u-fri'-tez. 

Indianapolis,  in-de-an-ap'-o-lis. 

Madrid,  mi-drid'.    (Spanish  pron.,  ma- 

Everest,  eV-fir-4st. 

Iowa,  i'-o-wa. 

dreed'.) 

Eyre,  air. 

Irrawaddy,  irs-ra-wad'-de. 

Magdalena,  mag-da-lee'-na. 

fate,  far,  fall,  fat,  me,  m 

St,  pine,  pin,  n&,  not,  organ,  berth,  firm,  sern 

ion,  tube,  tub,  thin,  this. 

168                                      PRONOUNCING   VOCABULARY. 

Maggiore,  mad-jo'-ra. 

P. 

San  Joaquin,  san  Ho-a-keen',  almost 

Malacca,  ma-lak'-ka. 

wah-keen'. 

Malay,  ma-la'. 

Pamir,  pa-meer'. 

Santa  Barbara,  san'-ta  baR-ba-ra. 

Maldive,  inal'-div. 

Pamlico,  pam'-lee-ko. 

Santa  Cruz,  san'-ta  kroos. 

Manitoba,  man-e-to'-ba.                   « 

Pampas,  pain'-pas. 

Santorini,  san-to-ree'-nee. 

Mantchooria,  inan-choo'-re-a. 

Panama,  pan-a-ma'. 

Sarmiento,  saR-me-en'-to. 

Maracaybo,  ma-ra-ki'-bo. 

Papua,  pap'-oo-a,  or  pa^-poo'-a. 

Saskatchewan,  sas-katch'-e-w&n. 

Marietta,  ma-re-et'-ta. 

Paraguay,  pa-ra-gwa',  or  pa-ra-gwi'. 

Scandinavian,  skan-de-na'-ve-an. 

Marquesas,  maR-ka'-sas.) 

Paramaribo,  par^-a-mar'-e-bo. 

Seine,  san,  or  s3n. 

Marseilles,  mar-salz'. 

Pasco,  pas'-ko. 

Senegal,  senv-e-gawl\ 

Mauna  Loa,  mow'-na  lo'-a. 

Patagonian,  pa-ta-go'-ne-an. 

Shasta,  shas'-ta. 

Mauritius,  maw-rish'-e-us. 

Paumotu,  pow-m6-too'. 

Siam,  si-am',  or  se-am\ 

Mediterranean,  m3dv-e-ter-ra'-ne-an. 

Peling,  pa* -ling'. 

Sicily,  sis'-il-e. 

Melbourne,  meT-burn. 

Persian,  per'-she-an. 

Sierra  Estrella,  se-eR'-Ra  gs-trel'-ya. 

Mesopotamia,  meV-o-po-ta'-me-a. 

Petchora,  petch'-o-ra. 

Sierra  Leone,  se-er'-ra  le-o'-nee. 

Michigan,  mish'-e-gan,  formerly  mish- 

Philippine,  fil'-ip-pin. 

Sierra  Madre,  se-en'-Ra  ma'-nra. 

e-gan'. 

Platte,  platt. 

Sierra  Nevada,  se-er'-ra  na-va'-Da. 

Mississippi,  misv-sis-sip'-pee. 

Polynesia,  por-e-nee'-she-a. 

Singapore,  singv-ga-pore\ 

Missouri,  mis-soo'-ree. 

Pompeii,  pom-pa'-yee. 

Sir,  or  Sihon,  sir,  or  seer,  see^-hon'. 

Mobile,  mo-beel'. 

Pontchartrain,  pont-char-tran'. 

Sitka,  sit'-ka. 

Moluccas,  mo-lfik'-kaz. 

Popocatepetl,  po-po-ka-ta-petl'. 

Spitzbergen,  spits-berg'-en. 

Monte  Rosa,  monv-ta-r6s'-sl. 

Prussia,  priish'-ya,  or  proo'-she-a. 

Steppes,  steps. 

Mont  Blanc,  mon8-bl6nB\ 

Pyrenees,  plr'-en-eez. 

St.  Louis,  sent  loo'-is,  or  sent  loo'-ee. 

Moosehead,  inoosx-hed\ 

St.  Petersburg,  sent  pee'-terz-burg. 

Moscow,  mos'-ko. 

St.  Roque,  sent  rok\ 

Q. 

St.  Thomas,  sent  tom'-as. 

Stromboli,  strom'-bo-le. 

N. 

Quebec,  kwe-beV. 
Quito,  kee'-to. 

Sumatra,  soo-ma'-tra. 
Sumbawa,  soom-baw'-wa. 

Nanling,  nanv-ling\ 

Suez,  soo'-fiz. 

Natchez,  natch'-iz. 

Suliman,  or  Suleiman,  soo-la-man'. 

Netherlands,  neTH'-er-landz. 

R. 

Syracuse,  slr'ra-kiiz. 

Neusalzwerk,  noi'-salts-verk. 

Syria,  slr'-e-a,. 

Nevada  de  Sorata,  ne-vah'-da  da  so- 
rl'-ta. 

Radack,  ra'-dak. 

Ralick,  ra'-lik. 

T. 

Newfoundland,  nu' -fond-land'. 

Ngami,  n'ga'-mee. 

Reading,  red'-ing. 
Rhine,  rin. 

Tahitian,  ta-hee'-tee-an. 

Niagara,    ni-ag'-a-rah,  originally   ne- 
a-ga'-ra. 

Rhone,  ron. 

Tanganyika,  tan-gan-ye'-ka. 

Riobamba,  re-o-bam'-ba. 

Tarim,  ta'-rem. 

Nicaragua,  nik-ar-a'-gwa. 

Rio  de  la  Plata,  ree'-o  da  la  pla'-ta. 
Rio  Grande,  ree'-o  gran'-da. 

Tasmania,  taz-ma-ne-a. 

Niemen,  nee'-men. 

Taurus,  taw'-rus. 

Nieuveldt,  nyuw'-velt. 

Rio  Janeiro,  ri'o  ja-nee'-ro. 

Tchad,  chid. 

Niger,  ni'-ger. 

Norfolk,  nor'-fok. 

Nova  Scotia,  no'-va  sko'-she-a. 

Nova  Zembla,  no'-va  zem'-bla. 

Nubia,  nu'-be-a. 

Roanoke,  rov-an-ok\ 

Teneriffe,  t5nv-er-iff'. 

Rodriguez,  rox-dreeg\ 
Russia,  rush'-i-a,  or  roo'-she-a. 

Thames,  temz. 
Thian-Shan,  teev-an'-shan. 

Russian  America,   roo'-shan   a-mer'- 

Thibet,  tib'-et,  or  tib-et'. 

e-ka. 

Timor,  te-mor'. 

N'yassa,  or  Nyassi,  ne-as'-see. 

Titicaca,  te-te-ka'-ka. 
Tocantins,  to-kan-teens'. 

s. 

Toledo,  to-lee'-do.     (Spanish  pron.,  to- 

o. 

la'-Do.) 

Sabine,  sa-been'. 

Tongan,  tong'-gan. 

Obe,  o'-bee. 

Saghalien,     sa-ga-lee'-an,    or    sa-ga- 

Torrens,  tor'-rens. 

Okefinokee,  ov-ke-fin-o'-kee. 

leen'. 

Torres,  toR'-Res. 

Okhotsk,    o-Kotsk'.      (Russian    pron., 

Sahara,  sa-ha'-ra,  or  sa'-ha-ra. 

Transylvanian,  tran-sil-va'-ne-an. 

o-Hotsk'.) 

Saint  Helena,  sant  hel-ee'-na. 

Trieste,  tre-est'. 

Onega,  o-na'-ga. 

Salina,  sa-li'-na. 

Trinidad,  trinv-e-dad\ 

Onimak,  oo-ne-mak'. 

Salzburg,  s&lts'-bfirg. 

Tristan  d' Acunha,tris'-tan  da-kun'-ya. 

Ontario,  on-ta'-re-o. 

Samoan,  sam-o'-an. 

Tundras,  toon'-dra. 

Oregon,  or'-e-gon. 

Sandwich,  sand'-wich,  or  sand'-wij. 

Tunis,  tu'-niss,  or  too'-niss. 

Orinoco,  or-e-no'-ko. 

San  Francisco,  san  fran-sis'-ko. 

Turkestan,  tooRv-kis-tan'. 

fate,  far,  fall,  fat,  me,  m 

5t,  pine,  pin,  nd,  not,  organ,  berth,  firm,  sern 

ion,  tube,  tub,  thin,  THis. 

PRONOUNCING  VOCABULARY. 


169 


u. 

w. 

Yaktusk,  yav-kootsh'. 

Yang-tse-Kiang,  yangx-tse-ke-ang\ 

Urumiyah,  oo-roo-mee' 

-ya. 

Wabash,  waw'-bash. 
Wasatch,  wav-saoh. 
Wener,  wa'-ner. 

Yeddo,  y8d'-do. 
Yellowstone,  yel'-lov-stone. 
Yenisei,  yfinv-e-sa'-e,  or  yeV-e-say'. 

Weser,  wev-zer.     (Ger.  pron.,  wa'-zer.) 

Yosemite,  yo-sem'-e-te. 

V. 

West  Indies,  west  in'-deez. 

Yucatan,  yoo-ka-tln'. 

Wetter,  wSt'-ter. 

Yukon,   yu'-kon. 

Valdai,  val'-dl. 

Winnebago,  winv-ne-ba' 

-go. 

Vancouvers,  van-koo'-vers. 

Winnipeg,  win'-e-peg. 

Venezuela,  v5nv-8z-wee 

'-la. 

Wisconsin,  wis-kon'-sin 

Vesuvius,  ve-su'-vi-us. 

Worcester,  woos'-ter. 

z. 

Vichy,  vee^-shee'. 

Vienna,  vS-en'-na. 

Zagros,  za'-gros\ 

Vindhya,  vlnd'-ya. 

y. 

Zambezi,  zam-ba'-zee. 

Volga,  vol'-ga. 

Zealand,ze'-land. 

Vosges,  vozh. 

Yabloni,  ya-blo-noi'. 

Zurrah,  zur'-ra. 

=^= 


BRIEF  ETYMOLOGICAL  VOCABULARY. 


Amazon,  "  Boat  destroyer." 
Arabia,  "  The  land  of  the  sunset." 
Brahmapootra,  "  The  son  of  Brahma." 
Cameroons,  "A  shrimp." 
Deccan,  "  The  south." 
Ecuador,  "  The  equator." 
Elton,  "Golden  lake." 
Formosa,  "  Beautiful "  (island). 
Gallapagos,  "  Islands  of  the  tortoises." 
Ganges,  "  Heavenward  flowing." 
Himalaya,  "  The  abode  of  snow." 

Hindostan,  "The  country  of  the  Hindoos,"  or  "Negro- 
land." 
Hoang-Ho,  "  Yellow  river." 
Holland,  "  Muddy  or  marshy  land." 
Irrawaddy,  "  The  great  river." 
Java,  "  Bice." 
Labrador,  "  Cultivable." 
Ladrones,  "  Islands  of  the  thieves." 
Lauterbriinnen,  "  Nothing  but  springs." 
Maldives,  "  Thousand  islands." 


Mantchooria,  "  Country  of  the  Mantchoos." 

Mer  de  glace,  "  Sea  of  ice." 

Mesopotamia,  "  Between  the  rivers." 

Mississippi,  "  The  great  water." 

Missouri,  "  Muddy  water." 

Netherlands,  "  The  low  countries." 

Niphon,  "  Fountain  or  source  of  light." 

Nova  Scotia,  "  New  Scotland." 

Nyassa,  "The  sea." 

Orinoco,  "  The  coiled  serpent." 

Papua,  "  Frizzled  hair." 

Patagonians,  "  Men  with  large  feet." 

Polynesia,  "  Many  islands." 

Popocatepetl,  "  Smoking  mountain." 

Saskatchewan,  "  Swift  current." 

Sierra  Nevada,  "  Snow-clad  mountain." 

Singapore,  "  City  of  the  lion." 

Staubbach,  "  Dust  or  mist  brook." 

Thian-Shan,  "  The  celestial  mountain." 

W!nnipiseogee,  "The  smile  of  the  great  Spirit." 

Yang-tse-Kiang,  "  Son  of  the  great  water." 


Statistical   Tables. 


►o^c 


Hydrographie  Table  of  the  Rivers  of  the 
World  (from  A.  K.  Johnston). 


Name  of  River. 


Rhine 

Vistula     .   .   •   < 

Elbe 

Oder 

Niemen    .   .  .   . 

Seine 

Nile 

Danube    .   .   .   . 
Dnieper    .   .   .   . 

Obi 

Yenisei    .   .  .  . 

Lena 

Volga 

Sir  or  Sihon  .   . 

Amoor 

Yang-tse-Kiang 
Hoang-Ho   .  .   . 

Ganges 

Indus    

Euphrates   .  .  . 
Irrawaddy  .  .  . 


Area  of  basin 

in  geographical 

square  miles. 


65,280 

56,640 

41,860 

39,040 

32,180 

22,620 
520,200  (?) 
234,080 
169,680 
924,800 
784,530 
594,400 
397,460 
237,920  (?) 
582,880 
547,800 
537,400 
432,480 
312,000  (?) 
195,680 
331,200 


Length  of 
stream  includ- 
ing windings. 


NEW  WORLD. 


St.  Lawrence  and  Great  Lakes 

Delaware 

Orinoco 

Amazon 

Tocantins    

San  Francisco 

La  Plata 

Mississippi 

Rio  del  Norte 

Mackenzie  . 

Saskatchewan 

Columbia 

Colorado 


297,600 

1,800 

8,700 

265 

252,000 

1,352  (?) 

1,512,000 

3,080 

284,480 

1,120 

187,200 

1,400 

886,400 

1,920 

982,400 

3,560 

180,000 

1,840  (?) 

441,600 

2,120 

360,000 

1,664 

194,400 

1,360 

170,000 

800  (?) 

600 

520 

684 

480 

460 

340 
2,240  (?) 
1,496 
1,080 
2,320 
2,800 
2,400 
2,400 
1,208  (?) 
2,380 
2,880 
2,280 
1,680 
1,960 
1,492 
2,200 


Areas  of  the  Principal  Lakes  of  the 
Earth.     (In  English  square  miles.) 


America. 

Area  sq.  m. 

Superior 28,600 

Michigan 26,000 

Huron 20,400 

Great  Slave 12,800 

Erie 9,600 

Winnipeg 9,600 

Georgian  Bay  ....    8,000 

Great  Bear 8,000 

Ontario 6,300 

Maracaibo 4,900 

Titicaca 4,200 

Athabasca 3,000 

Nicaragua 2,800 

Great  Salt 2,200 

Green  Bay 2,000 

Champlain 480 

Pontchartrain .   .    .   .      440 

Pyramid 360 

Moosehead 240 

Winnebago 212 

Europe. 

Ladoga 6,330 

Onega 3,280 

Wener 2,136 

Wetter 839 

Malar 763 


Area,  sq.  m. 

Geneva 326 

Constance 290 

Maggiore 152 

Asia. 
Caspian  Sea  ....  160,000 

Aral  Sea 88,000 

Baikal 13,000 

Balkash 8,600 

Zurrah(Afghanistan)    4,000 

Wan 2,200 

Urumiyah 1,800 

Lop 560 

Dead  Sea 400 

Tiberias 200 

Africa. 

Victoria  Nyanza  .   .  28,000 

Albert  Nyanza  .   .   .  26,000 

Tchad 15,000 

Tanganyika  ....  13,000 

Nyassa 5,000 

Australia. 

Eyre 3,000 

Torrens 2,600 

Gairdner 2,400 


Population  of  the  Earth. 

(From  Bradley's  Atlas.) 

America 100,415,400 

Europe 327,743,414 

Asia 795,591,000 

Africa 205,823,260 

Pacific  Islands _. 4,232,000 

Total 1,433,805,074 


170 


STATISTICAL  TABLES, 


171 


Tables  showing  the  Area  and  Product 
of  some  of  the  Cereals,  etc.,  in  the 
United  States. 

(From  the  Census  Reports  of  1880.) 
INDIAN  COEN. 

Acres.  Bushels. 

9,011,602      327,796,895 

6,616,364      276,093,295 

5,588,357      203,464,620 

3,679,247      117,121,915 


Stale. 

Illinois 

Iowa 

Missouri    .... 
Indiana     .... 

Ohio 3,297,342      112,681,046 

Kansas 3,417,700      106,791,482 

Kentucky 3,021,350      .....        73,977,829 

Nebraska 1,631,840      65,785,572 

Tennessee 2,905,038      62,833,017 

Pennsylvania.    .   .    .      1,374,241      47,970,987 


WHEAT. 

Illinois 3,218,963 

Indiana 2,619,307 

Ohio 2,556,134 

Michigan 1,822,752 

Minnesota 3,046,821 

Iowa 3,049,347 

California 1,837,322 

Missouri 2,074,314 

Wisconsin 1,948,036 


Pennsylvania 


.  .  .  51,136,455 

.  .  .  47,288,989 

.  .  .  46,014,869 

.  .  .  35,537,097 

.  .  .  34,625,657 

.  .  .  31,177,225 

.  .  .  28.787,132 

.  .  .  24,971,727 

.  .  .  24,884.689 

1,445,384      19,462,405 


OATS. 

Illinois 1,959,853 

Iowa 1,507,490 

New  York 1,261,171 

Pennsylvania ....  1,237,593 

Wisconsin 955,276 

Ohio 910,388 

Minnesota 617,427 

Missouri 968,473 

Michigan 536,167 

Indiana 623,600 


California 
New  York 
Wisconsin 
Iowa  .  .  . 
Minnesota 
Nebraska . 
Ohio  .  .  . 
Illinois  .  . 
Michigan  . 
Oregon  .   . 


Pennsylvania 
Illinois  .  .  . 
New  York  . 
Wisconsin  . 
Iowa  .... 
New  Jersey  . 
Kentucky  . 
Missouri  .  . 
Nebraska  .  . 
Kansas  .    .    . 


New  York  .  . 
Pennsylvania  . 
New  Jersey  .  . 
Michigan  .  .  . 
Maine  .  .  .  . 
Vermont  .  .  . 
Wisconsin  .  . 
West  Virginia 

Ohio 

Illinois  .    .    .    . 


BAELEY. 

586,045  . 

356,556  . 

204,323  . 

198,885  . 

116,024  . 

115,288  . 

57,485  . 

55,278  . 

54,509  . 

29,311  . 

EYE. 

398,465  . 

192,138  . 

244,894  . 

169,693  . 

102,580  . 

106,029  . 

89,579  . 

46,488  . 

34.372  . 
34,628  . 

BUCKWHEAT. 

291,228  . 

246,199  . 

35.373  . 
33,955  . 
20,135  . 
17,630  . 
34,119  . 
30,334  . 
22,130  . 
16,464  . 


63,206,250 
50,612,141 
37,575,506 
33,847,439 
32,911,246 
28,664,505 
23,372,752 
20,673,458 
18,190,493 
15,606,721 


12,578,486 
7,788,749 
5,043,202 
4,021,473 
2,973,061 
1,744,711 
1,707,164 
1,229,693 
1,204,523 
920,977 


3,683,621 

3,121,682 

2,634,390 

2,298,544 

1,518,307 

949,104 

676,245 

535,458 

424,693 

413,181 


4,461,200 
3,593,328 
466.414 
413,180 
382,701 
356,618 
299,150 
285,298 
280,229 
178,964 


Slate. 
Kentucky    .    . 
Virginia,  .    .    . 
Pennsylvania  . 

Ohio 

Tennessee  .  . 
North  Carolina 
Maryland  .  . 
Connecticut  . 
Missouri  .  .  . 
Wisconsin    .    . 


TOBACCO. 

Acres.  Pounds. 

226,127  171,121,134 

139,423 80,099,838 

27,567  36,957,772 

34,679  34,725,405 

41,532  29,365,052 

57,215  26,986,448 

38,174  26,082,147 

8,666  .....  14,044,652 

15,500  11,994,077 

8,811  10,878,463 


Population  of  the  United  States. 

(From  the  Census  of  1890.) 

North  Atlantic  States 17,401,545 

Maine 661,086 

New  Hampshire 376,530 

Vermont 332,422 

Massachusetts 2,238,943 

Ehode  Island 345,506 

Connecticut 746,258 

New  York 5,997,853 

New  Jersey 1,444,933 

Pennsylvania 5,258,014 

South  Atlantic  States 8,857,920 

Delaware 168,493 

Maryland 1,042,390 

District  of  Columbia 230,392 

Virginia 1,655,980 

West  Virginia 762,794 

North  Carolina 1,617,947 

South  Carolina  .    ., 1,151,149 

Georgia 1,837,353 

Florida 391,422 

North  Central  States 22,362,279 

Ohio 3,672,316 

Indiana !  2,192,404 

Illinois 3,826,351 

Michigan 2,093,889 

Wisconsin 1,686,880 

Minnesota 1,301,826 

Iowa 1,911,896 

Missouri 2,679,184 

North  Dakota 182,719 

South  Dakota 328,808 

Nebraska 1,058,910 

Kansas 1,427,096 

South  Central  States 10,972,893 

Kentucky 1,858,635 

Tennessee 1,767,518 

Alabama 1,513,017 

Mississippi 1,289,600 

Lf  .isiana 1,118,587 

Texas 2,235,523 

Indian  Territory 

Oklahoma  .    .    .    . 61,834 

Arkansas 1,128,179 

Western  States 3,027,613 

Montana 132,159 

Wvoming 60,705 

Colorado 412,198 

New  Mexico 153,593 

Arizona 59,620 

Utah 207,905 

Nevada 45,761 

Idaho 84,385 

Al'Lskji                                                 •    •••••••  — 

Washington    ........ 349,390 

Oregon 313,767 

California 1,208,130 

Total  population  of  the  United  States  ....  62,622,250 


172 


STATISTICAL  TABLES. 


Cities  of  the  United  States  having  a  Pop- 
ulation over  30,000,  in  order  of  Pop- 
ulation. 

(From  the  Census  of  1890.) 

NO.  CITIES.  POPULATION. 

1.  New  York  City,  N.  Y 1,513,501 

2.  Chicago,  111 1,098,576 

3.  Philadelphia,  Pa 1,044,894 

4.  Brooklyn,  N.  Y 804,377 

5.  St.  Louis,  Mo 460,357 

6.  Boston,  Mass 446,507 

7.  Baltimore,  Md 434,151 

8.  San  Francisco,  Cal 297,990 

9.  Cincinnati,  0 296,309 

10.  Cleveland,  0 261,546 

11.  Buffalo,  N.  Y 254,457 

12.  New  Orleans,  La 241,995 

13.  Pittsburgh,  Pa 238,473 

14.  Washington,  D.  C •  .    .   .  229,796 

15.  Detroit,  Mich 205,669 

16.  Milwaukee,  Wis 204,150 

17.  Newark,  N.  J 181,518 

18.  Minneapolis,  Minn 164,738 

19.  Jersey  City,  N.  J 163.987 

20.  Louisville,  Ky 161,005 

21.  Omaha,  Neb 139,526 

22.  Rochester,  N.Y 138,327 

23.  St.  Paul,  Minn 133,156 

24.  Kansas  City,  Mo 132,416 

25.  Providence,  E.  1 132,043 

26.  Indianapolis,  Ind 107,445 

27.  Denver,  Cal »   .   .   .   .  106,670 


NO.  CITIES.  POPULATION. 

28.  Allegheny  City,  Pa. 104,967 

29.  Albany,  N.  Y 94,640 

30.  Columbus,  0 90,398 

31.  Syracuse,  N.  Y 88,387 

32.  Worcester,  Mass 84,536 

33.  Scranton,  Pa 83,450 

34.  Toledo,  0 82,652 

35.  New  Haven,  Conn 81,451 

36.  Eichmond,  Va 80,838 

37.  Paterson,  N.  J 78,358 

38.  Lowell,  Mass 77,605 

39.  Nashville,  Tenn 76,309 

40.  Fall  Eiver,  Mass 74,351 

41.  Cambridge,  Mass 69,837 

42.  Atlanta,  Ga 65,514 

43.  Memphis,  Tenn 64,586 

44.  Grand  Eapids,  Mich 64,147 

45.  Wilmington,  Del 61,437 

46.  Troy,  N.  Y 60,605 

47.  Beading,  Pa 58,926 

48.  Dayton,  0 58,860 

49.  Trenton,  N.  J 58,488 

50.  Camden,  N.J 58,274 

51.  Lincoln,  Neb 55,491 

52.  Lynn,  Mass 55,684 

53.  Charleston,  S.C 54,592 

54.  Hartford,  Conn 53,182 

55.  St.  Joseph,  Mo •    .    .  52,811 

56.  Evansville,  Ind 50,674 

57.  Los  Angeles,  Cal 50,394 

58.  Des  Moines,  la 50,067 


MODEL  TEXT-BOOKS 

FOR 

SCHOOLS,  ACADEMIES  AND  COLLEGES. 


Chase  &  Stuart's  Classical  Series. 

FIRST  YEAR  IN  LATIN. 

A  LATIN  GRAMMAR. 

A  LATIN  READER. 

C/ESAR'S  COMMENTARIES.     With  Lexicon  and  Notes. 

FIRST  SIX  BOOKS  OF  /ENEID.     With  Lexicon  and  Notes. 

VIRGIL'S  /ENEID.     With  Notes. 

VIRGIL'S  ECLOGUES  AND  GEORGICS.    With  Lexicon  and  Notes. 

CICERO'S  SELECT  ORATIONS.     With  Lexicon  and  Notes. 

CICERO  DE  ORATORE.     With  Notes. 

CICERO  DE  SENECTUTE  ET  DE  AMICITIA.     With  Notes. 

CICERO  DE  OFFICIIS.     With  Notes. 

CICERO'S  TUSCULAN   DISPUTATIONS.    With  Notes. 

CICERO'S  SELECT  LETTERS.     With  Notes. 

HORACE'S  ODES,  SATIRES  AND  EPISTLES.     With  Notes. 

SELECTIONS  FROM  HORACE.  With  Lexicon  and  Notes.  (In  Prep.) 

SALLUST'S  CATALINE  ET  JUGURTHA.    With  Lexicon  and  Notes. 

LIVY.     With  Notes. 

CORNELIUS  NEPOS.     With  Lexicon  and  Notes. 

TERENCE.     With  Notes. 

TACITUS.    With  Notes. 

JUVENAL.     With  Notes. 

OVID.     With  Lexicon  and  Notes. 

PLINY.     With  Notes.     (In  Preparation.) 

A  Series  of  Text-Books  on  the  English  Language. 

BY  JOHN  S.  HART,  LL.D. 

LANGUAGE  LESSONS  FOR  BEGINNERS. 
AN  ELEMENTARY  ENGLISH  GRAMMAR. 
ENGLISH  GRAMMAR  AND  ANALYSIS. 
FIRST  LESSONS  IN  COMPOSITION. 
COMPOSITION  AND  RHETORIC. 

Hart's  Composition  and  Rhetoric  is  more  generally  in  use  than  any 
other  work  on  the  subject. 

The  practical  character  of  this  book  is  one  of  its  most  valuable 
features.  In  this  respect  it  is  far  ahead  of  any  other  work  of  its 
kind. 

Prof.  Moses  Coit  Tyler  says  of  it : 

"  In  the  transition  from  grammar  to  what  may  be  called  the  me- 
chanics of  literary  workmanship,  we  are  obliged  to  insist  upon  a 
particular  text-book — *  Hart's  Composition  and  Rhetoric' — simply 
because  that  book  is  the  only  one  as  yet  in  the  market  which  deals 
so  fully  and  so  well  with  the  topics  which  we  desire  to  emphasize." 

The  thousands  of  schools  of  every  grade,  including  Graded  Schools, 
Academies,  Seminaries,  High-Schools,  Normal  Schools,  Colleges, 
and  such  institutions  as  Vassar  College,  U.  S.  Military  Academy  at 
West  Point,  in  which  this  book  is  used,  not  only  with  satisfaction, 
but  with  enthusiasm,  testify  to  its  merit.  Unless  peculiarly  meri- 
torious, no  book  could  possibly  attain  the  widespread  popularity 
which  has  been  accorded  to  this  manual. 


Prof.  Houston's  Series  of  Text-Books. 

EASY  LESSONS  IN  NATURAL  PHILOSOPHY. 
INTERMEDIATE  LESSONS  IN  NATURAL  PHILOSOPHY. 
ELEMENTS  OF  NATURAL  PHILOSOPHY. 
ELEMENTS  OF  PHYSICAL  GEOGRAPHY. 

Webb's  Word -Analysis  Series. 

THE  MODEL  DEFINER. 
THE  MODEL  ETYMOLOGY. 
A  MANUAL  OF  ETYMOLOGY. 


CHRISTIAN  ETHICS;  or,  The  Science  of  the  Life  of  Human 
Duty.  A  New  Text-Book  on  Moral  Science.  By  Rev.  D.  S.  Gre- 
gory, D.  D. 

PRACTICAL  LOGIC.     By  Rev.  D.  S.  Gregory,  D.D. 

A  MANUAL  OF  ELOCUTION  AND  READING.  By  Dr.  Edward 
Brooks,  Principal  of  the  State  Normal  School,  Millersville,  Pa. 

LESSONS  IN  LANGUAGE.)     __  _ 

>     Bv  Edward  Gideon,  A.  M. 
EXERCISES  IN  ENGLISH./       y 

PRACTICAL  BOOK-KEEPING.    By  Prof.  John  Groesbeck,  author 
of  the  Crittenden  Commercial  Arithmetic.     In  two  books,  viz. : 
School  Edition,  Single  and  Double  Entry. 
College  Edition,  Single  and  Double  Entry. 

THE  CRITTENDEN  COMMERCIAL  ARITHMETIC  AND  BUSI- 
NESS MANUAL.  Designed  for  the  use  of  Academies,  High- 
Schools,  etc.     By  Prof.  John  Groesbeck.     Revised  Edition. 

AN  ELEMENTARY  ALGEBRA.  A  Text-Book  for  Schools  and 
Academies.     By  Joseph  W.  Wilson,  A.  M. 

A  HAND-BOOK  OF  LITERATURE.  By  E.J.  Trimble,  late  Prof. 
of  Literature  in  State  Normal  School,  West  Chester,  Pa. 

A  SHORT  COURSE  IN  LITERATURE.      By  E.  J.  Trimble. 

SHORT  STUDIES  IN  LITERATURE.  By  Albert  P.  Southwick, 
A.M. 

FIRST  LESSONS  IN  PHYSIOLOGY.  With  Special  Reference  to 
the  Effects  of  Alcohol,  Tobacco  and  other  Narcotics  on  the  Human 
System.     By  Charles  K.  Mills,  M.  D. 

ANATOMY,  PHYSIOLOGY  AND  HYGIENE.  With  Special  Refer- 
ence to  the  Effects  of  Alcohol,  Tobacco  and  other  Narcotics  on  the 
Human  System.     (In  Preparation.) 

THREE  THOUSAND  PRACTICE  WORDS.  By  Prof.  J.  Willis 
Westlake,  A.  M.,  State  Normal  School,  Millersville,  Pa. 

A  HAND-BOOK  OF  MYTHOLOGY.     By  S.  A.  Edwards. 

POLITICAL  ECONOMY.  A  Text-Book  for  Schools,  Academies  and 
Colleges.     (In  Preparation.) 

THE  GOVERNMENT  OF  THE  PEOPLE  OF  THE  UNITED 
STATES.  A  Text-Book  on  Civil  Government  for  Schools  and 
Academies.     By  F.  N.  Thorpe,  Ph.D. 

AMERICAN  LITERATURE.  A  Text-Book  for  Schools  and  Acada- 
mies.     By  A.  H.  Smyth,  A.  M. 

IN  THE  SCHOOL-ROOM;  or,  Chapters  in  the  Philosophy  of 
Education.     By  John  S.  Hart,  LL.D. 

THE    MODEL    POCKET    REGISTER    AND    GRADE-BOOK.      A 

Roll-Book,  Record  and  Grade-Book  combined. 

THE  MODEL  SCHOOL  DIARY.  Designed  as  an  aid  in  securing 
the  co-operation  of  parents.  It  consists  of  a  daily  Record  of  the 
Attendance,  Deportment,  Recitation,  etc.  of  the  Scholar. 

THE  MODEL  MONTHLY  REPORT.  Similar  to  the  Model  School 
Diary,  excepting  that  it  is  intended  for  a  Monthly  instead  of  a 
Weekly  Report  of  the  Attendance,  etc.  of  the  Pupil. 

MODEL  ROLL-BOOKS,  Nos.  I  and  2.  Designed  for  Recording 
Attendance,  Recitation,  etc.  Sample  Sheets  sent  by  mail  on  ap- 
plication. 


Manuals  for  Teachers. 

A  Series   of  Hand-books   in   five  volumes,  which,  it  is   believed,  will 
prove  a  valuable  contribution  to  the  Art  and  Science  of  Teaching. 

These  Manuals  have  been  received  with  remarkable  favor  by  teachers 
everywhere.     Descriptive  Circular  on  application. 

1.  THE  CULTIVATION  OF  THE  SENSES. 

2.  THE  CULTIVATION  OF  THE  MEMORY. 

3.  ON  THE  USE  OF  WORDS. 

4.  ON   DISCIPLINE. 

5.  ON  CLASS  TEACHING. 


OUR  BODIES.     A  Series  of  Charts  for  Teaching  Physiology,  etc.,  with  reference  to  the  Effects  of  Alcohol. 

For  further  information  respecting  our  Publications  please  address 

ELDREDGE   &   BROTHER, 

17  North  Seventh  Street, 

PHILADELPHIA,  PA. 


/ 


3*^ 


<&t& 


v 


^f 


I 


Qbu^ '  '^L" 


<v^A 


c 


/.  ' 


iJLi^J^- 


_ .  • 


{%-t- -  _  ^     yd  tf-uA^-tr-^t/-1     /^         >t- 


J> 

— 

7 

£ 

5 

/-/ 

* 

^^/>%2p% 


ja 


==3r 


.IB) 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 

t-p     n 

— 7TT 


once  Use 


LD  21-100m-9,'48(B399sl6)476 


£W, 


K 


